A supporter of Pompey, he is noted for being one of the consular generals who led Roman legions against the slave armies of Spartacus in the Third Servile War.
The first member of the Gellii to achieve the consulate, at an early age Lucius was attached to Gaius Papirius Carbo as his contubernalis.
He and his colleague also ensured that no Roman citizen in the provinces could be tried in absentia on a capital charge – an attempt to restrict the ravages of Gaius Verres in Sicily.
Having won a number of victories against ill-prepared Roman forces, the Senate now recognised Spartacus as a serious threat and sent both the consuls to confront the slave armies at the head of four legions.
[15] By 67 BC, Gellius was serving as a legate with praetorian imperium under Pompey, who had received an extraordinary command to rid the Mediterranean Sea of pirates.