Algardi, the son of a silk merchant from Bologna, was trained under Lodovico Carracci (Carracci, Lodovico) at the Accademia degli Incamminati, where he acquired the skills of a first-rate draftsman. After a short period of activity in Mantua (1622), he moved to Rome (1625), where he designed the stucco decorations in San Silvestro al Quirinale and gained some success as a restorer of classical sculptures. With the monument of Cardinal Millini (d. 1629) in Santa Maria del Popolo, the Frangipani monument in San Marcello al Corso, and the bust of Cardinal Laudivio Zacchia (Berlin), Algardi emerged as the principal rival of Gian Lorenzo Bernini (Bernini, Gian Lorenzo) in the field of portrait sculpture. Lacking Bernini's dynamic vitality and penetrating characterization, Algardi's portraits were appreciated for their sobriety and surface realism.

After the election of Pope Innocent X (1644), Algardi superseded Bernini in papal favour. Between this date and his death in 1654, Algardi produced some of his most celebrated works, among them the seated statue of the pope now in the Palazzo dei Conservatori (1645) and a colossal marble relief of the Meeting of Attila and Pope Leo in St. Peter's (1646–53), which influenced the development and popularization of illusionistic reliefs. Although he was generally less theatrical than Bernini, Algardi in this work effectively created a larger than life-size narrative whose principal events are dramatically conveyed. With his gesture of pushing away Attila, Leo points to the miraculously airborne Saints Peter (Peter the Apostle, Saint) and Paul (Paul, the Apostle, Saint), who have come to lend divine assistance. The deep shadows, emphatic gestures, and heavy drapery patterns work together to create an arresting and convincing sense of papal power. At this time Algardi also designed the Villa Doria Pamphili and a fountain in the Cortile di San Damaso of the Vatican.

Algardi's style is less ebullient and pictorial than Bernini's, and, even in such typically Baroque works as the tomb of Pope Leo XI in St. Peter's (1634–52) and the high altar of San Paolo at Bologna (1641), the restraining influence of the antique is strongly evident.