A.J. Barner played football at Aurora High School in Ohio. During his time at Aurora, he was a consensus 3-star recruit at tight end. He also played defense and as a linebacker was named the Northeast Ohio Division III Defensive Player of the Year. He finished his prep career with 15 receptions for 123 yards and 4 touchdowns and collected 124 tackles on defense. During his senior season, Barner committed to play football at Indiana.
As a freshman in 2020, Barner appeared in 8 games, primarily on special teams and was named special teams player of the week for his work against Michigan State.
In his sophomore year, Barner was a reserve tight end playing in 12 games, starting 1 and was a special teams contributor. Barner finished the season collecting 14 receptions for 162 yards and a touchdown for the Hoosiers.
In his junior season, Barner was selected as a team captain and backed that up with his best season to date. In 10 games, he caught 28 passes for 199 yards and 3 touchdowns. After the season, Barner entered the transfer portal and accepted an offer to play football at Michigan for Jim Harbaugh and the Wolverines.
This season, Barner hauled in 22 passes for 249 yards and 1 touchdown. His best performance came in a game against rival Michigan State where he had 8 receptions for 99 yards and a touchdown.