Fountain was drafted by the Indianapolis Colts in the fifth round, 159th overall, of the 2018 NFL draft.[4] He was waived on September 1, 2018, and was signed to the practice squad the next day.[5][6] On December 7, Fountain was promoted to the active roster.[7]
On August 19, 2019, Fountain was placed on injured reserve after undergoing ankle surgery.[8]
Fountain signed a one-year exclusive-rights free agent tender with the team on March 31, 2020.[9] He was waived on September 5, 2020, and signed to the practice squad the next day.[10][11] He was promoted to the active roster on September 16, 2020.[12] He recorded his first career reception in the Colts week 3 game against the New York Jets. The reception would be a 12-yard reception. He was waived on October 31, 2020,[13] and re-signed to the practice squad three days later.[14] He was elevated to the active roster on November 7 for the team's week 9 game against the Baltimore Ravens, and reverted to the practice squad after the game.[15] His practice squad contract with the team expired after the season on January 18, 2021.[16]
Kansas City Chiefs
Fountain signed with the Kansas City Chiefs on May 17, 2021.[17] He was released on October 12, 2021.[18] He signed to the practice squad on October 14, 2021.[19] He signed a reserve/future contract with the Chiefs on February 2, 2022.[20]
On August 30, 2022, Fountain was waived by the Chiefs[21] and signed to the practice squad the next day.[22] He was elevated to the active roster on September 10, 2022, via a standard elevation which caused him to revert back to the practice squad after the game.[23] He was released on October 24, 2022.[24]
Chicago Bears
On October 26, 2022, the Chicago Bears signed Fountain to their practice squad.[25] He signed a reserve/future contract on January 10, 2023.[26] He was released on August 29, 2023.[27]
Detroit Lions
On August 31, 2023, Fountain was signed to the Detroit Lions practice squad.[28] He signed a reserve/future contract on January 31, 2024.[29] He was released on August 27, 2024.[30]