The Fiji-born back, who is a reconnaissance tank soldier with the Royal Scots Dragoon Guards, impressed during a recent trial at the Recreation Ground.
"Roko caught the eye playing for the Army at Twickenham earlier in the year, and continued to do so when he came on trial," said Bath coach Gary Gold.
"We believe he has the ability to play professional rugby, and the Army has supported his desire to test himself at this level while he is still a serving soldier.
"He is strong, quick, and very committed, both during games and training, and we're looking forward to having him in the squad."
Rokoduguni has scored seven tries in two appearances for the Army's rugby side.