The sophomore Allen was competing against heralded freshman Kyler Murray for the starting job.
Aggies coach Kevin Sumlin announced Allen would get the nod when A&M opens the season Sept. 5 against the Sun Devils in Houston.
Allen played in nine games last season for Texas A&M as a freshman and started the final five. He passed for 1,322 yards and 16 touchdowns with seven interceptions. In Texas A&M's Liberty Bowl victory against West Virginia, Allen passed for a season-best 294 yards and four touchdowns.