His later career is described by Tacitus. In 52 he was made governor of Britain, following the death in office of Ostorius Scapula, at a time when the situation was deteriorating as a result of a string of rebellions. The south-east was securely held, but despite the defeat of Caratacus the previous year, the tribes of what is now Wales, particularly the Silures, continued to hold out. Venutius' first insurrection against Queen Cartimandua of the Brigantes occurred during Didius' rule and he despatched troops under Caesius Nasica to aid her.
Didius acted to quell the rebels rather than enlarge the empire during his rule, which lasted until AD 57. Although criticised by Tacitus as being reactive and defensive, he was probably acting on instructions from Claudius who did not consider the benefits of further conquest in difficult terrain to be great enough to warrant the risk. Instead, Didius built roads and forts at the borders such as those at Usk to contain the barbarians. After five years in the post, covering the last two years of the reign of Claudius and the first three of Nero, Didius was replaced by Quintus Veranius.
Quintilian tells us that, after several years of campaigning for a provincial governorship, Didius complained at the province he was offered, although whether this refers to Sicily or Britain is unknown. The orator Domitius Afer sarcastically advised him to think of his country. The next governor of Britain, Quintus Veranius, says on his tombstone that he took the job "although he did not seek it", which has been interpreted as a barbed comment on Didius.