On December 31, 2013, it was announced that Allen had signed a homegrown contract with Real Salt Lake of Major League Soccer.[2] He made his professional debut on March 8, 2014, against the LA Galaxy, in which he came on in the 90th minute for Joao Plata as Salt Lake won 1–0.[3] On March 29, 2015, after coming on as a substitute in a match against Toronto FC, he scored his first professional goal in the 90th minute, just moments after Toronto had tied the game in a 2–1 win.
After playing over 40 games in his first two full seasons, Allen's progress has been hampered by injury, only playing two matches since the end of the 2016 season.[4]
Allen retired from playing professional soccer at the end of the 2019 season due to injury problems.[5]