He was born as Servius Sulpicius Galba near Terracina, "on the left as you go towards Fundi" in the words of Suetonius. Through his paternal grandfather ("more eminent for his learning than for his rank — for he did not advance beyond the grade of praetor" and who "published a voluminous and painstaking history", according to Suetonius), who predicted his rise to power, he was descended from Servius Sulpicius Galba. Galba's father attained the consulship, and although he was short, hunchbacked and only an indifferent speaker, was an industrious pleader at the bar. His mother was Mummia Achaica, the granddaughter of Catulus and great - granddaughter of Lucius Mummius Achaicus. They only had one other child, an elder son called Gaius who left Rome after squandering the greater part of his estate, and committed suicide because Tiberius would not allow him to take part in the allotment of the provinces in his year. On his father's remarriage to Livia Ocellina, Galba was adopted by her and took her names, remaining Lucius Livius Ocella Sulpicius Galba until becoming emperor.

He came from a noble family and was a man of great wealth, but was unconnected either by birth or by adoption with the first six Caesars. In his early years he was regarded as a youth of remarkable abilities, and it is said that both Augustus and Tiberius prophesied his future eminence (Tacitus). His wife, however, was connected at least by the marriage of some of her relatives to some of the Julii - Claudii. The couple had two sons, Galba Major and Galba Minor who died during their father's life. Galba Major was the elder son and born circa 25 AD. Hardly anything is known about his life as he died young. He was engaged to his stepsister Antonia Postuma, but they never wed, which leads modern historians to believe that he died during this time. Their engagement is dated to 48, and that is generally believed to be his time of death. Galba Minor was the younger son. His date of birth was later than 25 but before 30. This Galba outlived his older brother, but did not live a long time. He was a quaestor in 58, but he was never seen in politics after that. Suetonius mentions that "Galba Minor had discovered his father's affair with a male slave and threatened to tell his stepmother, which led to death of him." His time of death is generally believed to be around 60 AD. Galba Minor was never married and had no children.

In addition, Suetonius's description of Galba was that In sexual matters he was more inclined to males, and then none but the hard bodied and those past their prime. This seems to be the only case in Roman history where a named individual male is stated to prefer adult males.

He became Praetor in 20, and consul in 33; he earned a reputation in the provinces of Gaul, Germania, Africa and Hispania (Iberia, comprising modern Spain and Portugal) for his military capability, strictness and impartiality. On the death of Caligula, he refused the invitation of his friends to make a bid for the empire, and loyally served Claudius. For the first half of Nero's reign he lived in retirement, until 61, when the emperor bestowed on him the province of Hispania Tarraconensis. In the spring of 68, Galba was informed of Nero's intention to put him to death, and of the insurrection of Julius Vindex in Gaul. He was at first inclined to follow the example of Vindex, but the defeat and suicide of the latter renewed his hesitation.

The news that Nymphidius Sabinus, the Praetorian Prefect, had given him his favour revived Galba's spirits. Until now, he had only dared to call himself the legate of the senate and Roman people; after Nero's suicide, he assumed the title of Caesar, and marched straight for Rome.

Following Nero's death, Nymphidius Sabinus sought to seize power prior to the arrival of Galba, but he could not win the loyalty of the Praetorian guard and was killed. Upon Galba's approach to the city in October, he was met by soldiers presenting demands; Galba replied by killing many of them.

Galba's primary concern during his brief reign was restoring state finances, and to this end he undertook a number of unpopular measures, the most dangerous his refusal to pay the praetorians the reward promised in his name. Galba scorned the notion that soldiers should be "bribed" for their loyalty. He further disgusted the populace by his meanness and dislike of pomp and display. Advanced age destroyed his energy, and he was entirely in the hands of favourites. Three of these — Titus Vinius, who became Galba's colleague as consul, Cornelius Laco, the commander of the Praetorian Guard, and Galba's freedman Icelus Marcianus — were said to virtually control the emperor. The three were called "The Three Pedagogues" because of their influence on Galba. All this made the new emperor gravely unpopular.

On 1 January 69, two legions in Germania Superior refused to swear loyalty to Galba. They toppled his statues, demanding that a new emperor be chosen. On the following day, the soldiers of Germania Inferior also rebelled and took the decision of who should be the next emperor into their own hands, proclaiming the governor of the province, Vitellius, as emperor. This outbreak of revolt made Galba aware of his own unpopularity and of the general discontent. In order to check the rising storm, he adopted as his coadjutor and successor L. Calpurnius Piso. The populace regarded the choice of successor as a sign of fear and the Praetorians were indignant, because the usual donative was not forthcoming.

M. Salvius Otho, formerly governor of Lusitania, and one of Galba's earliest supporters, disappointed at not being chosen instead of Piso, entered into communication with the discontented Praetorians, and was adopted by them as their emperor. Galba at once set out to meet the rebels, though he was so feeble that he had to be carried in a litter. He was met by a troop of Otho's cavalry and was killed near Lacus Curtius. One guard, centurion Sempronius Densus, died defending him. Piso was killed shortly afterwards. According to Plutarch, during Galba's last moments he offered his neck, and said, "Strike, if it be for the good of the Romans!" According to Suetonius, Galba prior to his death had put on a linen corset — although remarking that it had little protection against so many swords. After his death, Galba's head was brought to Otho, who gave it to his camp followers who paraded and mocked it — the camp followers' mocking was their angry response to a remark by Galba that his strength was unimpaired. The head was then bought by a freedman so he could throw it on the place where his former master had been executed on Galba's orders. Galba's steward buried both head and trunk in a tomb by the Aurelian Road.

Altogether, around 120 people claimed the credit for killing Galba, being anxious to win Otho's favour and hoping to be rewarded. A list of their names was drawn up, which fell into the hands of Vitellius when he succeeded Otho as emperor. Every one of them was executed.

During the later period of his provincial administration, Galba was indolent and apathetic, but this was due either to a desire not to attract Nero's favor or to the growing infirmities of age. Tacitus says all pronounced him worthy of the empire, until he became emperor ("omnium consensū cāpax imperiī nisi imperasset").