He played college football for the Iowa State Cyclones and was selected by the Chicago Bears in the third round of the 2019 NFL draft.

Growing up in the Cincinnati, Ohio area, he is an Eagle Scout[1] in addition to being a standout prep dual threat quarterback.

[11] At the conclusion of the season Montgomery was named to the honorable mention Freshman All-American team by Campus Insiders.

[14] Montgomery led the nation in forced missed tackles with 104, breaking the previous record of 89 set by Dalvin Cook.

[23] Montgomery started the season slow, but had a string of four straight 100-yard games with five touchdowns from mid-September to mid-October, and ended the season with another string of three straight 100-yard games with six touchdowns, including 179 yards from scrimmage in the 2018 Alamo Bowl loss to Washington State.

[25] On January 7, 2019, Montgomery announced that he would forgo his final season of eligibility and declare for the 2019 NFL draft.

[26] ESPN2 dubbed Montgomery the "Frankenstein" of running backs for possessing similar physical traits of different NFL running backs, including the footwork of Saquon Barkley, the field vision of Le'Veon Bell, the strength of Ezekiel Elliott and the athleticism of Sony Michel.

[32] In Week 2 against the Denver Broncos, Montgomery rushed 18 times for 62 yards and his first career NFL touchdown as the Bears won 16–14.

Before the regular season began, head coach Matt Nagy emphasized the offense would prioritize establishing a run game.

[38] He opened the season with 64 rushing yards on 13 attempts en route to a 27–23 comeback win against the Detroit Lions.

[42] Montgomery returned for the Bears' Week 12 match-up against the Packers on Sunday Night Football, where he totaled 143 yards from scrimmage and recorded a receiving touchdown in a 41–25 loss.

[44] In Week 14 against the Houston Texans, he amassed 113 rushing yards, including an 80-yard touchdown run on the first play of the Bears' opening offensive possession.

[48] In Week 17 against the Green Bay Packers, Montgomery recorded 132 yards from scrimmage and a rushing touchdown during the 35–16 loss.

[69] In Week 15's matchup against the Buffalo Bills, Montgomery suffered an MCL injury, which was initially believed to require a season-ending surgery.

He does not know his father, and his mother moved the family numerous times around Cincinnati due to economic hardship.

He remembers using the oven for heat, and boiling water collected from gas stations in the bath tub when either was disconnected.

After scoring a touchdown, Montgomery frequently holds up a "V"-sign in memory of a high school teammate and role model who was murdered during a home invasion.

[25] While he was with Iowa State, Montgomery was chosen as a semi-finalist for the Jason Witten Collegiate Man of the Year Award for his efforts in befriending Hunter Erb, a 6-year-old who was born with multiple congenital heart defects, and orchestrating a team visit to Marshalltown, Iowa to help clean up after a tornado.

After the Lions' Thanksgiving win in 2024, he drew media attention for eating a carrot while his teammates ate CBS' celebratory turkey.