Ellefson played college football at North Dakota State. During his senior season, Ellefson caught 15 passes for 199 yards and five touchdowns.[2] He was also a noted blocker during the team's running game. Ellefson finished his college career with 35 receptions for 463 yards and 16 touchdowns, a program record for tight ends.[3]
Ellefson went undrafted in the 2020 NFL draft, and was signed by the Jacksonville Jaguars.[5][6] He was waived during final roster cuts on September 5, 2020,[7] and signed to the team's practice squad the next day.[8] He was elevated to the active roster ahead of the team's 2020 season opener against the Indianapolis Colts on September 12,[9] and reverted to the practice squad after the game.[10] He was elevated again on September 19 for the team's week 2 game against the Tennessee Titans, and reverted to the practice squad after the game.[11] He was placed on the practice squad/COVID-19 list by the team on October 17, 2020,[12] and was activated back to the practice squad on October 22.[13] He was promoted to the active roster on October 22.[14] He was placed on injured reserve on December 5.[15]
On August 31, 2021, Ellefson was waived by the Jaguars.[16]
Minnesota Vikings
On September 1, 2021, Ellefson was claimed off waivers by the Minnesota Vikings.[17] He was placed on injured reserve on October 28 with knee and foot injuries.[18] He was activated on January 8, 2022.[19]
On October 8, 2022, Ellefson was placed on injured reserve.[20] He was activated on November 30. He was placed back on injured reserve on December 7.[21]
On June 1, 2023, Ellefson announced his retirement from professional football.[22]
Coaching career
Five days after retiring as a player, Ellefson was added to the Vikings' coaching staff as an Offensive Assistant.[23]