Claudius spent much of his early adult life outside the center of Roman government, pursuing historical and scholarly interests while relatives held imperial power. He became consul under Caligula in 37 CE. When Caligula was assassinated in 41, the Praetorian Guard supported Claudius as emperor, establishing his position before the Senate accepted it. Ancient portrayals emphasize his physical difficulties and supposed weakness, but those accounts were written within political and literary traditions that can distort assessment of his administration.

Claudius extended the empire and developed its government. The invasion of Britain began in 43 under Aulus Plautius, and Claudius traveled there briefly to participate in the conclusion of the initial campaign. Roman control expanded over subsequent years rather than encompassing the entire island immediately. Other changes incorporated territories into the provincial system. His administration promoted public works, including aqueducts, a harbor near Ostia, and an ambitious drainage project at Lake Fucinus whose engineering limitations created difficulties.

The emperor relied heavily on imperial freedmen to manage correspondence, finance, and petitions. Their influence provoked hostility among senators, but it also reflected the increasing complexity of administration. Claudius heard legal cases, issued decisions, and extended citizenship, including support for admitting leading men from Gaul to senatorial participation. Parts of his speech on that question survive on the Lyon Tablet, providing evidence beyond hostile narrative biography. His rule nevertheless involved executions, political suspicion, and repeated conflicts with members of the elite.

Dynastic and household struggles became central to the reign's later years. His wife Messalina was executed in 48 after a crisis described in ancient accounts as a conspiracy involving another marriage. Claudius then married his niece Agrippina the Younger and adopted her son Nero, placing him in a strong position relative to Claudius's own son Britannicus. Claudius died in 54, and Nero succeeded. Ancient authors commonly attributed the death to poisoning arranged by Agrippina, but the accusation cannot be treated as conclusively proven. His career demonstrates both expansion and institution building within an imperial system vulnerable to military intervention, elite opposition, and succession conflict.