Gunnar Helm attended Cherry Creek High School in Greenwood Village, Colorado and played tight end for four years. During Helm's junior season, he hauled in 33 receptions for 411 yards and seven touchdowns. As a senior, he had 28 receptions for 367 yards and seven touchdowns. Coming out of high school, Helm was rated a three-star recruit, where he held offers from schools such as Alabama, Auburn, Colorado State, and Texas. He committed to play football at the University of Texas.
Helm played in 12 games as a true freshman in 2021 and did not record a catch. In 2022, he started four of 13 games and hauled in five receptions for 44 yards. As a junior, Helm played in 14 games with six starts and recorded 14 receptions for 192 yards and two touchdowns.