Galba was the son of the consul Gaius Sulpicius Galba and Mummia Achaica, and in addition to great wealth and ancient lineage he enjoyed the favour of the emperors Augustus and Tiberius. He began his senatorial career before the normal age, became consul (AD 33), received command of the Upper German army (40–42), and served a proconsulship in Africa (44–45).

Galba was appointed governor of Nearer Spain in 60 and served in that post for eight years. In 68, believing that the emperor Nero was planning his assassination, Galba accepted (and perhaps even prompted) an invitation from Vindex (Vindex, Gaius Julius), the governor of Lugdunensis in Gaul, to head a rebellion against Nero. He then recruited an additional new legion in Spain and built up a large following in many other regions of the empire, though Vindex himself was defeated in a battle with the Rhine armies. The praetorian prefect, Gaius Nymphidius Sabinus, encouraged the imperial guard (the Praetorian Guard) to desert Nero for a large reward, and on June 9, 68, Nero committed suicide.

Accompanied by Otho, the governor of Lusitania, Galba marched on Rome and was proclaimed emperor by the Senate. Galba's attempt to cut back Nero's extravagant spending was unpopular, as was his execution of troops recruited by Nero as well as those of several opponents, including Lucius Clodius Macer, whose revolt against Nero from Africa had cut off Rome's grain supply. Galba's refusal to pay the praetorians the promised donative led to the assassination of his ally Nymphidius. Galba rewarded the parts of Gaul that had supported Vindex and thus outraged the legions of Upper Germany, which had defeated Vindex. On Jan. 1, 69, the legions of Upper Germany refused the customary vote of allegiance to Galba and soon joined with the legions of Lower Germany in proclaiming Vitellius (Vitellius, Aulus) emperor. To win senatorial support, Galba chose as his heir a scion of a noble Roman family, Lucius Calpurnius Piso Frugi Licinianus, instead of Otho, who had been his loyal ally. Otho won over the praetorians with the promise of a donative, and they murdered Galba and Piso in the Roman Forum on January 15. The historian Tacitus famously wrote of Galba, “It was everyone's opinion that he was capable of ruling the empire, had he never ruled” (Histories, Book I, part 49).