Draft and minor leagues (2015–2019) in 2017 The
Cincinnati Reds selected Stephenson in the first round, 11th overall, of the
2015 MLB draft. He had previously committed to play
college baseball for
Georgia Tech, but chose to forego that commitment in favor of signing with Cincinnati. After signing professionally, Stephenson was assigned to the
Rookie-level Billings Mustangs of the
Pioneer League. He played in 54 games for Billings, batting .268 with one home run and 16 RBI in 194
at bats. He began the 2016 season with the
Dayton Dragons in the
Low-A Midwest League, where he batted .196 in 25 games before going on the
disabled list with a wrist sprain at the end of May. After completing a five-game rehabilitation assignment with the
Arizona League Reds, Stephenson rejoined the Dragons on July 13. He finished the season batting .278 in 139 at bats, with three home runs and 16 RBI in 39 Midwest League games. Stephenson rejoined the Dragons for the 2017
Minor League Baseball season. He suffered a season-ending injury on July 14, when he injured a ligament in his thumb while sliding into a base. At the time of the injury, Stephenson had been batting .278 in 295 at bats, with six home runs and 50 RBI in 80 games. In the last 10 of those games, he batted .355 with 11
hits, seven
runs scored, and three RBI in 31 at bats. Stephenson was promoted to the
Class A-Advanced Daytona Tortugas of the
Florida State League for the 2018 season. He remained fully healthy throughout the season but was uneven at the plate: Stephenson batted .351 through the first half of the minor league season but only .188 in August. He batted .250 for the season, with 11 home runs and 59 RBI in 388 at bats across 109 games, The Reds'
farm system promoted Stephenson to the
Double-A Chattanooga Lookouts of the
Southern League for the 2019 minor league season. In 89 games and 312 at bats there, Stephenson batted .285 with six home runs and 44 RBI, In a survey of Southern League managers conducted by
Baseball America, Stephenson was also named the league's best defensive catcher. After the season, the Reds sent Stephenson, who had
platooned the catcher position with
Chris Okey, to the
Arizona Fall League to continue his development. He batted .347 in 13 games for the
Glendale Desert Dogs, with seven
doubles and three RBI, and received the Dernell Stenson Sportsmanship Award as the player who "best exemplifies unselfishness, hard work, and leadership" in the Arizona Fall League. That November, the Reds added Stephenson to their
40-man roster to protect him from the
Rule 5 draft.
Cincinnati Reds (2020–present) in 2021 Stephenson was slated to begin the 2020 season with the
Triple-A Louisville Bats, but the changes to the
2020 MLB season caused by the
COVID-19 pandemic meant that he was instead one of several
prospects assigned to an alternate training site in
Prasco Park, where he could be promoted in case of injury or illness to
Tucker Barnhart or
Curt Casali. The Reds sustained a number of injuries and illnesses at the beginning of their pandemic-abbreviated season, and Stephenson was promoted to make his MLB debut on July 26, 2020. Relieving Casali in the seventh inning, he hit a home run on the second pitch he saw, a
fastball from
Duane Underwood Jr. of the
Chicago Cubs. It was the third time in franchise history that a Red had hit a home run in their first major league
plate appearance, and the first time since
Ted Tappe did so against the
Brooklyn Dodgers on September 14, 1950.
Pinch-hitting for
leadoff hitter Shogo Akiyama in the first game of a
doubleheader on September 14, Stephenson hit his first
walk-off home run to win 3–1 against the
Pittsburgh Pirates. Stephenson was used sparingly during the 2020 season, batting .294 with two home runs, four runs scored, and six RBI in eight games. He had hoped to join the Reds for the
2020 National League Wild Card Series against his hometown Atlanta Braves, The Braves won the Wild Card,
shutting out the Reds twice in the best-of-three series and eliminating them from the playoffs. The offseason departure of Curt Casali allowed Stephenseon to appear on the Reds' 2021
Opening Day roster alongside Tucker Barnhart. The left-handed Barnhart started more often against right-handed
starting pitchers, while the right-handed Stephenson received more playing time against southpaw pitchers. Stephenson also spent time at
first base in May after an injury to
Joey Votto. Regular playing time in the middle of the
batting order during Votto's injury seemed beneficial for Stephenson, who batted .316 over a seven-game span in Votto's absence, and Bell promised to find Stephenson opportunities to bat even in games he did not start that season. He was a successful pinch hitter when not catching, going 9-for-35 with two doubles, three home runs, and 12 RBI in pinch-hitting situations by September 10. The Reds fell short of postseason contention, finishing seven games behind the
St. Louis Cardinals in the Wild Card race, but Stephenson had a strong rookie season, batting .286 with 10 home runs and 45 RBI. He additionally led all rookie catchers with a .797
on-base plus slugging (OPS) and was named to the MLB All-Rookie First Team. Stephenson received two third-place votes in balloting for NL
Rookie of the Year, an award which was won by Cincinnati teammate
Jonathan India. The Reds traded Barnhart to the
Detroit Tigers during the 2021–22 offseason, with
general manager Nick Krall telling reporters that the move allowed Stephenson to become Cincinnati's everyday catcher in 2022. On April 19, Stephenson sustained a
concussion when
Luke Voit of the
San Diego Padres collided with him at home plate: Voit was attempting to score on the play, while Stephenson was tagging him out. He returned two weeks later after clearing concussion protocols. Stephenson was injured again on June 10, fracturing his right thumb on a
foul tip off the bat of
Jordan Luplow during Cincinnati's game against the
Arizona Diamondbacks. He was activated from the 10-day injured list on July 9 and returned to his role as everyday catcher. On July 22, Stephenson fractured his right
clavicle on a foul tip off the bat of St. Louis Cardinals hitter
Paul Goldschmidt. Stephenson required surgery to repair the fracture, which effectively ended his season. To ease Stephenson back into playing, the Reds planned to have Stephenson catch 65 games in 2023, with Curt Casali and
Luke Maile taking the rest of the workload. On days he did not catch, Stephenson would play first base or serve as Cincinnati's
designated hitter. This plan was abandoned by the end of May, with manager David Bell telling reporters that learning first base was "a lot to handle" for a young player like Stephenson. Stephenson's 2023 season was a step back offensively: he batted .243 with 13 home runs over 142 games, and he saw a decrease in power from the past two years. He also struggled defensively, particularly with
pitch framing, and young pitchers like
Hunter Greene and
Andrew Abbott preferred to work with Maile, which limited Stephenson's playing time towards the end of the season. He hit his career-high 14th home run of the season on August 6 against the
Miami Marlins. In addition to his power, Stephenson increased his plate discipline, focusing on making hard contact, while also enhancing his framing as a catcher. Stephenson also put more time into studying opponents and personally working with the pitching staff, improving his rapport with his batterymates. ==Personal life==