With the defeat and death of Pompey in 48 BC, Libo attached himself to Pompey's son, Sextus Pompey. Sextus was Libo's son-in-law due to his marriage to Libo's daughter Scribonia. In 40 BC, Sextus sent him as an unofficial envoy to Mark Antony in Greece, seeking an alliance against Octavian (later known as Augustus), who had just defeated Antony's partisans in the Perusine War, and was instrumental in forming an alliance between the two. Octavian attempted to drive a wedge between Sextus Pompey and Mark Antony by marrying Libo's sister, Scribonia. In the subsequent Pact of Misenum, Libo acted as an important negotiator; in return for his support, Sextus managed to extract from Octavian the promise of a future consulate for Libo.