Sullivan attended St. Thomas More High School in Rapid City, South Dakota, where he played quarterback for the football team. He was team captain and team MVP, and was named to the All-State and Academic All-State teams.[1]
Sullivan joined the South Dakota Mines Hardrockers program in NCAA Division II, where he became the starting quarterback.[2] In his four years at SDSM&T he set 17 new school records, 2 All-RMCS best quarterback and Don Hansen All-American Team.[3][4] With 325.1 yards per game, he led the entire NCAA Division II. In total he completed 293 passes for 3,576 yards, 32 passing touchdowns and 10 rushing touchdowns.
In December 2018, Sullivan signed with the Marburg Mercenaries ahead of the 2019 German Football League season.[6] In his first year as an import player he reached several milestones. After nine victories out of 14 games his team qualified for the play-offs, where they lost in the quarterfinals against the Dresden Monarchs. He was nominated in the GFL Allstar Team as the statistical passing leader of this season. He threw for 46 passing touchdowns and ran for 14 rushing touchdowns. In October 2019 he was signed by the Vienna Vikings in the Austrian Football League.[7] He did not start due to the COVID-19 pandemic.[1]
European League of Football
In the inaugural 2021 European League of Football season Sullivan was signed by the Frankfurt Galaxy and head coach Thomas Kösling.[8][1] In the regular season Sullivan had the highest passing completion rate (66,2 %) of the league as well as 2,037 passing yards and 23 touchdowns. With a passer rating of 105.96 he was the second best quarterback in the regular season.[9] In the Divisional Championship playoff-game against the Cologne Centurions he scored five passing touchdowns with four different target and was nominated MVP of this game. In the first ELF Championship game the Frankfurt Galaxy won against the Hamburg Sea Devils with a dramatic 32:30 score. He was nominated ELF Championship game-MVP, voted to the ELF Allstar game and won the Offensive Player of the Year award.[10] The Frankfurt Galaxy announced in mid November the extension for another season.[11] Sullivan was released by the Galaxy on November 7, 2023.[12]