Personally, I always thought he went to a regional or sectoral academy and was commissioned as an officer of the local moff and not the Empire proper; that explains the goofy uniform he wears when he visits Tatooine. (One of the action figures claims it's an "Academy outfit," but Biggs had to have already graduated by this point, or else there isn't enough time for him to be posted and defect before Yavin.) Remember that Biggs isn't too keen on restoring the Republic; he simply wants a reformed Empire. Whose side would Biggs be flying on after Endor?
Personally, I always thought he went to a regional or sectoral academy and was commissioned as an officer of the local moff and not the Empire proper; that explains the goofy uniform he wears when he visits Tatooine. (One of the action figures claims it's an "Academy outfit," but Biggs had to have already graduated by this point, or else there isn't enough time for him to be posted and defect before Yavin.) Remember that Biggs isn't too keen on restoring the Republic; he simply wants a reformed Empire. Whose side would Biggs be flying on after Endor?