He was proconsul in Greece from 210 to 206, conducting the First Macedonian War against Philip of Macedon. Galba was notable for leading the first Roman fleet into the Aegean Sea and capturing Aegina (210), but otherwised achieved little, and most of the fighting was done by the Greek allies of Rome.
He was dictator in 203, and elected consul again in 200, when he led in the Second Macedonian War. He landed at Apollonia in a scheme to invade Macedonia from the west, defeated Philip at Ottolobus, but then retired to Illyria. Although the campaign was considered only a minor military success, it did convince the Aetolians to ally with Rome.
In 197 and 196, Galba was one of ten senatorial commissioners helping Titus Flamininus settle political issues in Greece, and ambassador to Antiochus III the Great in 193.