Jennings played at Tennessee from 2015 to 2019 under head coaches Butch Jones and Jeremy Pruitt.[6] He converted to wide receiver in college.[7]
In the 2015 season, Jennings was an instant contributor. In his collegiate debut against Bowling Green, Jennings had three receptions for 56 yards in the 59–30 victory.[8] Later on in the season, in a 28–27 loss to rivalFlorida, he showed off his dual-threat ability when he threw a 58-yard touchdown pass to quarterback Joshua Dobbs on a trick play.[9]
In the 2016 season, Jennings's role in the offense expanded. He recorded his first game with over 100 receiving yards with three receptions for 111 yards and a touchdown in a 38–28 victory over Florida sealing an 18-point comeback for the Vols.[10] The win was Tennessee's first over the Gators since the 2004 season.[11] In the next game against rivalGeorgia, Jennings recorded the game-winning reception on a 43-yard Hail Mary from Dobbs to put the Vols 34–31 with no time remaining.[12] Jennings finished the 2016 season with 40 receptions for 580 yards and seven touchdowns.[13]
In 2017, Jennings appeared in only one game due to a wrist injury but was dismissed from the team under interim head coach Brady Hoke later in the season.[14] Jennings was reinstated for the next season by then-new head coach Jeremy Pruitt for the 2018 season.[15][16] Jennings earned a medical redshirt for his time missed in the 2017 season.[17] In the 2018 season, Jennings appeared in 11 games and recorded 30 receptions for 438 yards and three touchdowns.[18]
In the 2019 season, Jennings was a key contributor for the Vols during their 8–5 season.[19] He recorded four games with at least 100 receiving yards. Jennings' best output came in a victory against South Carolina, where he had seven receptions for 174 yards and two touchdowns.[20] Overall, Jennings finished his senior season with 59 receptions for 969 yards and eight touchdowns.[21]
During his collegiate career, Jennings had 146 receptions for 2,153 yards and 18 touchdowns.[22]
Jennings was selected by the San Francisco 49ers in the seventh round with the 217th overall pick of the 2020 NFL draft.[25] He was waived on September 5, 2020, and signed to the practice squad the next day.[26][27] Jennings was placed on the practice squad/injured list on October 24.[28] He signed a reserve/future contract on January 4, 2021.[29]
Over the course of the 2021 season, Jennings established himself as the 49ers third wideout. He registered his first NFL touchdown in Week 2 against the Philadelphia Eagles, and by the end of November had become an integral part of the offense.[30] Over the final five weeks of the 2021 season, Jennings recorded 16 receptions for 212 yards and three touchdowns, including a career-high six receptions for 94 yards and two touchdowns in a must-win week 18 matchup with the Los Angeles Rams.[31] His production continued in the playoffs, with Jennings recording at least one reception in each round before the 49ers exited in the National Football Conference (NFC) Championship.[32]
In the 2022 season, Jennings appeared in 16 games, of which he started four. He finished the 2022 season with 35 receptions for 416 yards and a touchdown.[33]
On February 28, 2023, the 49ers placed an exclusive-rights tender on Jennings, which he signed in April.[34][35] In the 2023 season, Jennings appeared in 13 games and started two. He had 19 receptions for 265 yards and one touchdown.[36] In Super Bowl LVIII, Jennings caught four of his five targets for 42 yards and a touchdown.[37] He also threw a 21-yard touchdown pass to Christian McCaffrey in a 25–22 overtime loss to the Kansas City Chiefs.[38] Jennings became the second player in Super Bowl history to throw for a touchdown and catch a touchdown, joining Nick Foles in Super Bowl LII.[39]
On March 11, 2024, the 49ers placed a tender on Jennings.[40] On May 29, Jennings signed a two–year, $15.4 million contract extension with the 49ers.[41] In Week 3, he had 11 receptions for 175 yards and three touchdowns in a 27–24 loss to the Los Angeles Rams.[42]