Gulussa became the King of Numidia along with his two brothers around 148 BC and reigned as part of a triumvirate for about three years.

In 148 BC, Masinissa, feeling that he was near death, consulted with Scipio Aemilianus regarding the settlement of his state.

Resuscitating, perhaps, a Libyan custom which shared the authority between three persons, Scipio Aemilianus established the three legitimate surviving sons as kings: Micipsa, Gulussa and Mastanabal.

Micipsa, the eldest, was in charge of the administration; it was to him that Masinissa had given his ring which, judging from the stelae of the Abizar style, was a sign of power.

But the Carthaginians, exasperated by the successive annexations of Masinissa, refused to enter into negotiations and even ambushed the princes on their return from Carthage.