Monteverdi, the son of a barber-surgeon and chemist, studied with the director of music at Cremona cathedral, Marcantonio Ingegneri, a well-known musician who wrote church music and madrigals of some distinction in an up-to-date though not revolutionary style of the 1570s. Monteverdi was obviously a precocious pupil, since he published several books of religious and secular music in his teens, all of them containing competent pieces in a manner not far from that of his master. The culmination of this early period occurred in two madrigal books published by one of the most famous of Venetian printers in 1587 and 1590. They are full of excellent, attractive works, somewhat more modern in approach than Ingegneri's, perhaps the result of studying the madrigals of Luca Marenzio (Marenzio, Luca) (1553–99), the greatest Italian madrigalist of the time, and others. As yet, however, Monteverdi's aim appeared to be to charm rather than to express passion; it is exemplified at its best in such a madrigal as the well-known setting of the poem “Behold the Murmuring Sea” by Torquato Tasso (Tasso, Torquato).

It is not known exactly when Monteverdi left his home town, but he entered the employ of the Duke of Mantua in about 1590 as a string player. He immediately came into contact with some of the finest musicians, both performers and composers, of the time. Most influential on him seems to have been the Flemish composer Giaches de Wert, a modernist who, although no longer a young man, was still in the middle of an avant-garde movement in the 1590s. The crux of his style was that music must exactly match the mood of the verse and that the natural declamation of the words must be carefully followed. Since he chose the highly concentrated, emotional lyric poetry of Tasso and Tasso's rival Battista Guarini (Guarini, Battista), Wert's music also became highly emotional, if unmelodious and difficult to sing. It had an immediate effect on Monteverdi, whose next book of madrigals, published in his first year at Mantua, shows the influence of the new movement on him, though his understanding was imperfect. It represented a complete change of direction for him. The melody is angular, the harmony increasingly dissonant, the mood tense to the point of neurosis. Guarini is the favoured poet, and every nuance of the verse is expressed, even at the expense of musical balance.

The new style and ambience seems to have upset his productivity. Although he went on composing, he published little for the next 11 years. In 1595 he accompanied his employer on an expedition to Hungary and four years later to Flanders. In about 1599 he married a singer, Claudia Cattaneo, by whom he had three children, one of whom died in infancy. When the post of maestro di cappella, or director of music, to the Duke became vacant on the death of Wert in 1596, Monteverdi was embittered at being passed over, but in 1602 he achieved the position, at the age of 35. He published two more books of madrigals in 1603 and 1605, both of which contain masterpieces. The avant-garde manner was now better assimilated into his idiom. While his aim was still to follow the meaning of the verse in great detail, he solved the purely musical problems of thematic development and proportion. Although the dissonances became more severe and the melody sometimes still more angular, the total effect was more varied in emotion and less neurotic. If Guarini's eroticism stimulated a sensual musical style, Monteverdi often gave his mature madrigals a lightness and humour, seeing the essence of a poem rather than its detail.

It was the advanced musical means, especially the use of intense and prolonged dissonance, that provoked attacks by the conservatives on Monteverdi, who became a figurehead of the avant-garde group. The attacks by a Bolognese theorist, Giovanni Maria Artusi, in a series of pamphlets, made Monteverdi the most famous composer of the age and provoked him to reply with an important aesthetic statement of his view on the nature of his art. He disclaimed the role of revolutionary, saying that he was only the follower of a tradition that had been developing for the last 50 years or more. This tradition sought to create a union of the arts, especially of words and music, so that he should not be judged simply as a composer using conventional musical devices. Moreover, the artwork must be powerful enough to “move the whole man,” and this again might mean the abandonment of certain conventions. On the other hand, he declared his faith in another and older tradition, in which music was itself supreme, and which was, in effect, represented by the pure polyphony of such composers as Josquin des Prez and Palestrina (Palestrina, Giovanni Pierluigi da). Thus, there were two “practices,” as he called them; and this view, which became immensely influential, was to prove the basis of the preservation of an old style in certain types of church music, as opposed to a modern style in opera and cantatas, a dichotomy that can be found well into the 19th century.

If the madrigals of this time gave him a reputation well outside northern Italy, it was his first opera, Orfeo, performed in 1607, that finally established him as a composer of large-scale music rather than of exquisite miniature works. Monteverdi may have attended some of the performances of the earliest operas, those composed by the Florentine composers Jacopo Peri (Peri, Jacopo) and Giulio Caccini (Caccini, Giulio), and he certainly had written some stage music in previous years. In Orfeo he showed that he had a much broader conception of the new genre than did his predecessors. He combined the opulence of dramatic entertainments of the late Renaissance with the straightforwardness of a simple pastoral tale told in recitative, which was the ideal of the Florentines. His recitative is more flexible and expressive than theirs, based on the declamatory melody of his madrigals rather than on their theories about heightened speech. Above all, he had a greater gift for dramatic unity, shaping whole acts into musical units, rather than assembling them from small sections. He also showed a sense of matching the climaxes in the drama by musical climaxes, using dissonance, the singer's virtuosity, or instrumental sonorities to create the sense of heightened emotion.

A few months after the production of Orfeo, Monteverdi suffered the loss of his wife, seemingly after a long illness. He retired in a state of deep depression to his father's home at Cremona, but he was summoned back to Mantua almost immediately to compose a new opera as part of the celebrations on the occasion of the marriage of the heir to the duchy, Francesco Gonzaga, to Margaret of Savoy. Monteverdi returned unwillingly and was promptly submerged in a massive amount of work. He composed not only an opera but also a ballet and music for an intermezzo to a play. Further disaster occurred when the opera, L'Arianna, was in rehearsal, for the prima donna, a young girl who had been living in Monteverdi's home, possibly as a pupil of his wife, died of smallpox. Nevertheless, the part was re-cast, and the opera was finally produced in May 1608. It was an enormous success. The score has been lost, except for the famous “Lamento,” which survives in various versions and is the first great operatic scena (i.e., a scene of especially dramatic effect, usually with arias).

After this enormous effort, Monteverdi returned again to Cremona in a condition of collapse, which seems to have lasted for a long time. He was ordered back to Mantua in November 1608 but refused to go. He eventually returned, but thereafter he hated the Gonzaga court, which he maintained had undervalued and underpaid him, though he gained a raise in pay and a small pension for his success with L'Arianna. He does not, however, appear to have been uncreative, though the music he wrote in the next year or so reflects his depression. He arranged the “Lamento” as a five-voiced madrigal and wrote a madrigalian threnody on the death of his prima donna. The sestina, published later in the sixth book of madrigals, represents the peak of dissonant, agonized music in this style. In a more vigorous vein, he wrote some church music, which he published in 1610 in a volume containing a mass in the old style and music for Vespers on feasts of the Blessed Virgin Mary. The mass was a remarkable achievement, a deliberate attempt to show that the polyphonic idiom was still possible when everywhere it was dying. Still more remarkable is the Vespers music, a virtual compendium of all the kinds of modern church music possible at the time—grand psalm settings in the Venetian manner, virtuoso music for solo singers, instrumental music used for interludes in the service, even an attempt to use up-to-date operatic music to set the expressive, emotional words of the Magnificat. Yet, though this music is as “advanced” as possible, Monteverdi makes it an extension of the old tradition by using plainsong tunes—ancient unaccompanied liturgical chants—as the thematic material for the psalms and Magnificats. Above all, this is music of the Counter-Reformation; using all means, traditional and new, secular and religious, it is designed to impress the listener with the power of the Catholic Church and its Maker.

When the maestro di cappella—that is, the director of music—of St. Mark's in Venice died, Monteverdi was invited to take his place, after an audition of some of his music in the basilica (San Marco Basilica). He finally took up his appointment in the autumn of 1613.

He was appointed largely because the musical establishment of St. Mark's was in need of an experienced director after some years of decline. The last of the native Venetian composers of any distinction, Giovanni Gabrieli (Gabrieli, Giovanni), had recently died. Although Monteverdi had not been primarily a church musician, he took his duties extremely seriously and within a few years completely revitalized the music in the basilica. He hired new assistants (including two future composers of note, Francesco Cavalli and Alessandro Grandi (Grandi, Alessandro)), wrote much church music, and insisted on daily choral services. He also took an active part in music making elsewhere in the city, directing the music on several occasions for the fraternity of S. Rocco, an influential philanthropic brotherhood, on the annual festival of its patron saint.

His letters in those early years in Venice reveal a complete change in his state of mind from what it was in Mantua. He felt fulfilled and honoured, well (and regularly) paid, and he seems to have been reasonably prolific. He kept up his links with Mantua, largely because there was little chance of producing opera in Venice, while opportunities came quite regularly from the Gonzaga court. In his correspondence, a philosophy of dramatic music emerges that was not only to mold Monteverdi's later work but also to influence the history of opera in general. The older type of opera had developed, on the one hand, from the Renaissance intermezzo—a short, static musical treatment, often allegorical and with scenery, of a subject from the play with which it was given, emphasizing the wishes of the gods; and, on the other hand, from the pastoral, with its highly artificial characterizations of shepherds and shepherdesses. Monteverdi, however, was increasingly concerned with the expression of human emotions and the creation of recognizable human beings, with their changes of mind and mood. Thus, he wished to develop a greater variety of musical means, and in his seventh book of madrigals (1619) he experimented with many new devices. Most were borrowed from the current practices of his younger contemporaries, but all were endowed with greater power. There are the conversational “musical letters,” deliberately written in a severe recitative melody in an attempt to match the words. The ballet Tirsi e Clori, written for Mantua in 1616, shows, on the contrary, a complete acceptance of the simple tunefulness of the modern aria.

His attempt to create a practical philosophy of music went on throughout the 1620s, leading to still further stylistic innovations. Following ideas derived from Plato, he divided the emotions into three basic kinds: those of love, war, and calmness. Each of these could be expressed by differing rhythms and harmonies. A further ingredient in his theories was a frank acceptance of realism—the imitating of the sounds of nature in various ways. All these ideas are to be found in his dramatic cantata, The Combat of Tancredi and Clorinda (1624), a setting of a section of Tasso's “Gerusalemme Liberata.” In this work, the rapid reiteration of single notes in strict rhythms and the use of pizzicato—plucking strings—to express the clashing of swords show important steps forward in the idiomatic use of stringed instruments.

These trends were continued in a comic opera, Licoris Who Feigned Madness, probably intended for the celebrations of the accession of Duke Vincenzo II of Mantua in 1627. The score has been lost, but a sizable correspondence survives. At this time, Monteverdi suffered more anxiety since his elder son, Massimiliano, was imprisoned in Bologna, where he was a medical student, for reading books banned by the Inquisition. It took some months before he was finally cleared of the charge. In the same year, 1628, Monteverdi also fulfilled a commission to write music for the intermezzi to Tasso's L'Aminta and for a tournament given in Parma in celebration of the marriage of Duke Odoardo Farnese to Margherita de' Medici.

Monteverdi and his family seemed to have emerged unscathed from the plague that broke out in 1630, and Monteverdi himself took holy orders during this period. He wrote a grand mass for the thanksgiving service in St. Mark's when the epidemic was officially declared over in November 1631. The “Gloria” from it still survives and shows him applying some of the theories concerning the diversity of mood suggested by the words. Both this and some other church music probably written about this time, however, show a calm and majestic approach rather than the passion of his earlier years. A book of lighthearted songs and duets published in the following year is much the same. There is also a detached quality about much of the music in the final collection of his madrigals assembled by Monteverdi himself in 1638. A vast retrospective anthology of music dating from 1608 onward, it sets out to display Monteverdi's theories, as its title, Madrigals of War and Love, denotes.

Though this collection, put together when Monteverdi was more than 70 years old, might seem the end of his career, chance played a part in inspiring him to an Indian summer of astonishing productivity: the first public opera houses opened in Venice in 1637. As the one indigenous composer with any real experience in the genre, he naturally was involved with them almost from the beginning. L'Arianna was revived again, and no fewer than four new operas were composed within about three years. Only two of them have survived in score—The Return of Ulysses to His Country and The Coronation of Poppea—and both are masterpieces. Although they still retain some elements of the Renaissance intermezzo and pastoral, they can be fairly described as the first modern operas. Their interest lies in revealing the development of human beings in realistic situations. There are main plots and subplots, allowing for a great range of characters—the nobility, their servants, the evil, the misguided, the innocent, the good. The music expresses their emotions with astonishing accuracy. Monteverdi shows how the philosophy of music evolved during his early years in Venice could be put to use, using all the means available to a composer of the time, the fashionable arietta (i.e., a short aria), duets, and ensembles, and how they could be combined with the expressive and less fashionable recitative of the early part of the century. The emphasis is always on the drama: the musical units are rarely self-contained but are usually woven into a continual pattern, so that the music remains a means rather than an end. There is also a sense of looking toward the grand climax of the drama, which inspires a grand scena for one of the main singers, Ulisse, Nero, or Poppea. At the same time, there are enough memorable melodies for the opera to seem musically attractive.

With these works Monteverdi proved himself to be one of the greatest musical dramatists of all time. That he was held in the highest esteem by his Venetian employers is shown by their gifts of money in these last years and by their granting him leave to travel to his native city in the last few months of his life. The Venetian public showed its esteem at his funeral, when after his death following a short illness, he was buried in the Church of the Frari, where a monument to him remains.