He has previously played in MLB for the Cincinnati Reds, Colorado Rockies, Pittsburgh Pirates, and Tampa Bay Rays.

Stephenson's senior season for the high school's baseball team began with two consecutive no-hitters.

[5] He was invited to participate in the 2010 Aflac All-America Game; Stephenson was named the starting pitcher for the West Team and pitched two scoreless innings.

[3] Baseball America rated Stephenson as one of the Reds' top ten prospects before the 2012 season, despite his not having made his professional debut.

[13] After pitching to a 5–3 win–loss record and a 2.57 ERA with 96 strikeouts in 77 innings, he was promoted to the Bakersfield Blaze of the High–A California League on July 18.

[14] Less than a month later, after pitching to a 2–2 record and a 3.05 ERA with Bakersfield, the Reds promoted Stephenson to the Pensacola Blue Wahoos of the Double–A Southern League in August,[1] as Reds' general manager Walt Jocketty said the team wanted to "fast track" Stephenson, whom he called "very impressive".

[22] On April 4, with Homer Bailey beginning the season on the disabled list the Reds added Stephenson to their Opening Day roster.

In his second start, against the Colorado Rockies Stephenson became the first Reds pitcher to complete seven innings up to that point in the 2016 season, allowing just three hits and one earned run while striking out three and walking two.

In 2019, Stephenson was used as a relief pitcher He appeared in 57 games, all out of the bullpen, and enjoyed career bests in ERA (3.76), WHIP (1.036), K/9 (11.3), BB/9 (3.3), and H/9 (6.0).

[28] On November 25, 2020, Stephenson and Jameson Hannah were traded to the Colorado Rockies in exchange for Jeff Hoffman and Case Williams.

[33] On June 2, 2023, the Pirates traded Stephenson to the Tampa Bay Rays in exchange for Alika Williams.

[38] Stephenson and his wife married in 2017, with fellow Reds pitcher Sal Romano serving as the best man.