Like all the kings of his dynasty except his father and grandfather, Hammurabi bore a tribal Amorite name belonging to the Amnanum. Only scanty information exists about his immediate family: his father, Sin-muballit; his sister, Iltani; and his firstborn son and successor, Samsuiluna, are known by name.

When Hammurabi succeeded Sin-muballit about 1792 BC he was still young, but, as was customary in Mesopotamian (Mesopotamia, history of) royal courts of the time, he had probably already been entrusted with some official duties in the administration of the realm. In that same year Rim-Sin of Larsa, who ruled over the entire south of Babylonia, conquered Isin, which served as a buffer between Babylon and Larsa. Rim-Sin later became Hammurabi's chief rival.

The reconstruction of Hammurabi's rule is based mainly on his date formulas (years were named for a significant act the king had performed in the previous year or at the beginning of the year thus named). These show him engaged in the traditional activities of an ancient Mesopotamian king: building and restoring temples, city walls, and public buildings, digging canals, dedicating cult objects to the deities in the cities and towns of his realm, and fighting wars. His official inscriptions commemorating his building activities corroborate this but add no significant historical information.

The size, location, and military strength of the realm left to Hammurabi made it one of the major powers in Babylonia. That Hammurabi was not strong enough to change the balance of power by his own will is well expressed in a diplomatic report: “There is no king who is powerful for himself: with Hammurabi, ‘the man of Babylon,' go 10 or 15 kings, so with Rim-Sin, ‘the man of Larsa'; with Ibalpiel, ‘the man of Eshunna,' . . . go 20 kings.”

Hammurabi inherited one major direction for his political activity: to succeed in controlling the Euphrates waters—important in an area that depended exclusively on irrigation agriculture. Such a policy naturally led to conflicts with the kingdom of Larsa, which was situated in a disadvantageous downstream position. This policy, begun by Hammurabi's great-grandfather but most forcefully and partially successfully pursued by his father, Hammurabi himself took up in 1787 BC, near the beginning of his reign, when he conquered the cities Uruk ( Erech) and Isin, held by Rim-Sin, and clashed again with Rim-Sin the year after. But, according to Hammurabi's date formulas and contemporary diplomatic correspondence, these operations led no further because Hammurabi shifted the direction of his military operations in 1784 toward the northwest and the east. For almost 20 years thereafter no significant warlike activity is reported. These years were characterized by changing coalitions among the main kingdoms—Mari, Ashur, Eshnunna, Babylon, and Larsa. Hammurabi used this time of uneasy stalemate to fortify several cities on his northern borders (1776–1768 BC).

The last 14 years of Hammurabi's reign were overshadowed by continuous warfare. In 1764 Hammurabi dealt with a coalition of Ashur, Eshnunna, and Elam—the main powers east of the Tigris—whose position threatened to block his access to the metal-producing areas of Iran. It can be assumed, however, that Hammurabi took the initiative in moving against Rim-Sin of Larsa in 1763 BC. Few particulars are reported about this latter war, but it seems that Hammurabi successfully employed a stratagem that apparently had been used before by Sin-muballit against Rim-Sin: damming up the water of a main watercourse and then either releasing it suddenly to create a devastating flood or simply withholding it—the main resource of life—from the enemy's people (that Hammurabi used this device to bring about Rim-Sin's defeat can be assumed from the fact that in 1760 he rebuilt a canal—the western branch of the Euphrates—to facilitate the resettlement of the uprooted population that lived along its course before this war). The final siege of Larsa, Rim-Sin's last stronghold, lasted for several months. It was the last step to Hammurabi's victory.

In 1762 BC Hammurabi again engaged in hostilities with the eastern powers. It is unknown whether this was a protective move on his part or a reaction on theirs to the change in the balance of power. The motives that led Hammurabi in 1761 BC against his longtime ally, Zimrilim, king of Mari, 250 miles (400 km) upstream from Babylon on the Euphrates, remain enigmatic. Two explanations are likely: it was either again a fight over water rights or an attempt by Hammurabi to gain control over Mari's excellent location at the crossroads of the ancient Middle East's overland trade.

Two years later Hammurabi had to direct his armies eastward for a third time (1757–55 BC). The final destruction of Eshnunna during this campaign—again achieved by damming up the waters—most likely proved to be a pyrrhic victory, because it removed a buffer zone between Babylonia proper and the peoples of the east (among them probably the Kassites, who were to take over in Babylonia 160 years hence). During his last two years, Hammurabi thus had to concentrate on the construction of defense fortifications. By this time he was a sick man, and he died about 1750 BC, with the burden of government already being carried by his son, Samsuiluna.

Changes affecting nearly all spheres of life took place during Hammurabi's reign. They were aimed at the consolidation of conditions resulting from the transformation of a small city-state into a large territorial state. His letters show that he personally engaged in the details of implementing these changes and in the daily routine of the administration of his realm. This personal style is characteristic for Hammurabi (Hammurabi, Code of) and also for other contemporary rulers. Hammurabi's laws—not a law code in the modern sense—must also be considered as an expression of his concern to be a just ruler—an ideal pursued by Mesopotamian kings at all times.

That Hammurabi failed to set up an effective bureaucratic system may be attributed to his personal style in the governance of his realm and the fact that he was fully engaged in wars during the last part of his reign. The lack of effective administration might have been one reason for the fast deterioration after his death of what he had achieved in military terms.

When Hammurabi conquered southern Babylonia he did not follow the century-old tradition of having himself deified during his lifetime. There is reason to believe that this was his personal decision, probably based on a different view of the nature of kingship, setting a precedent for the concept of kingship until Hellenistic times.

Hammurabi's eminence in Mesopotamian history has long been exaggerated. It was first based on the discovery of his laws but subsequent discoveries of older, though less voluminous, collections of laws have led to a less enthusiastic view. Moreover, the frequently noted resemblance between Hammurabi's laws and the Mosaic laws is now seen in terms of common heritage rather than as proof for direct dependency.

Hammurabi is also credited with bringing Mesopotamia again under a single rule. Although there existed certain trends toward such unification—particularly expressed in the themes depicted on contemporary seals and in the apodoses of omens evoking a past when such kings as Sargon of Akkad and Shulgi ruled Mesopotamia from the Persian Gulf to the Mediterranean Sea—it is doubtful that unification was the only motive for Hammurabi's conquests. The lasting achievement of Hammurabi's rule was that the theatre of Mesopotamian history, which had been in the south from the beginning of the 3rd millennium BC, was shifted to the north, where it remained for more than 1,000 years.