The Elder Balbus was born c. 100 BCE of a noble family in Gades, in southern Spain. He served with the Roman military in the Sertorian War (79-72 BCE), commanded by Q. Metellus Pius and Pompey. At its conclusion he came to Rome as a protege of Pompey and, in recognition of his bravery, was awarded citizenship by Pompey, which was confirmed under the lex Gellia Cornelia of 72 BCE. He took his Roman name from one of the Cornelii Lentuli, either his commander in Spain or his sponsor in Rome. Enrolled in the order of equites, he acquired a villa in Tusculum, becoming a neighbor and friend of Cicero.

In 61 BCE Caesar, as propraetor of Further Spain, took Balbus, now his protege, with him as his praefectus fabrum or "chief builder," a post to which Balbus was appointed by Caesar again in 58. As such he secured numerous benefits for his home town of Gades and was celebrated as a benefactor.

Noted for his political savvy and his great wealth, Balbus helped in various ways to build the coalition of Pompey and Caesar in 60 BCE which became the Triumvirate; later, as agent, he managed Caesar's interests in Rome while he was on campaign in Gaul.

Having earned enemies through his prominent association with Pompey and Caesar, in 56 BCE he found himself charged by a fellow-townsman from Gades, under the lex Papia of 64 BC, for illegally claiming Roman citizenship. He was successfully defended by Pompey, Crassus, and Cicero, whose speech, given last, survives, the Pro Balbo. A man of literary interests about which he corresponded with Cicero, he published a diary, now lost.

Although he claimed neutrality in the civil war between Pompey and Caesar (and tried to persuade Cicero to do likewise), he actually supported Caesar and became very influential after the Caesarian victory at Pharsalus.

In 44 BCE Balbus gave his support to Octavian as Caesar's heir, and was rewarded for this by his election to the consulship, becoming Rome's first foreign-born consul in 40 BCE.

Wealthy beyond all others, in his will he left 25 denarii to each citizen of Rome; to his namesake, Balbus Minor, he left a tradition of distinguished political involvement.