"Your father was an Imperial Senator and a friend of Bail Organa, wasn't he?" "Yes, sir. I wanted to join the rebellion with Leia, but my father had other ideas."
―Tycho Celchu and Beruss, the former reviewing Beruss's history.[src]
During his time at the Illodian Officers' Academy, Beruss developed skills as a starpilot and sharpshooter. After graduating with honors, Beruss was slated to represent Illodia in the 0 BBYImperial Games as a sharpshooter, until they were cancelled due to Alderaan's destruction.
While his father encouraged Beruss to join the Illodian defense force, he instead chose to join the Rebel Alliance, ignoring his father's fears of Imperial reprisal against his homeworld.
Details of Beruss's early work with the Alliance is unclear, but he was offered a position in Rogue Squadron shortly before the Battle of Brentaal IV c. 4.4 ABY, despite having only completed two combat missions prior.
During his tenure with Rogue Squadron, Beruss served as Soontir Fel's wingman and fell in love with fellow pilot Feylis Ardele.
Beruss presumably continued to fly with Rogue Squadron until the unit's disbandment in 5.5 ABY.