Stevenson spent 2016 playing for the High-A Potomac Nationals and Class-AA Harrisburg Senators. In 133 combined games, he compiled a .276 batting average with three home runs, 34 RBIs, and 39 stolen bases. After the season, Stevenson was one of a handful of Nationals prospects to play in the Arizona Fall League. Playing for the Glendale Desert Dogs,[13] he led the AFL in hits with 30 and posted a .353 batting average, second in the league,[14] and was named along with Desert Dogs and Senators teammate Drew Ward[broken anchor] to the 2016 AFL Top Prospects Team.[15]
Stevenson received an invitation to major league camp in the 2017 season. He played well, impressing Nationals manager Dusty Baker, who remarked of the outfielder, "He's always ready. When I look down there, he's already looking at me."[19] Stevenson was reassigned to minor league camp on March 13.[20]
Stevenson in 2017
After beginning his season with Class-AA Harrisburg and hitting .316 in April, Stevenson was promoted to the Class-AAA Syracuse Chiefs.[21] Stevenson struggled in the early going with Syracuse, hitting just .169 over his first 31 games before turning his game around.[22] After amassing a .246 batting average overall as a Chief, Stevenson was promoted to the major leagues on July 23, 2017, after outfielders Chris Heisey and Ryan Raburn were placed on the disabled list and bereavement list, respectively.[23] He made his major league debut the same day, pinch-hitting and coming in on a double switch in the sixth inning to play left field. On July 27, Stevenson notched his first major league hit, lining a pitch into right field off Hernán Pérez of the Milwaukee Brewers — a utility player pitching in the major leagues for the first time, with his team trailing by 13 runs in the bottom of the eighth inning — for a single.[24] The following month, on August 10, he made a diving catch down the left field line to take away an RBI and extra bases from Miami Marlins second baseman Dee Gordon with two outs in the top of the ninth, preserving a 3–2 lead in the game as Nationals closer Sean Doolittle locked down the save.[25] On August 27, Stevenson recorded his first major league RBI with a go-ahead, bases-loaded walk against the New York Mets that gave the Nationals a 5-4 victory.[26][27] On August 28, the Nationals optioned Stevenson back to Syracuse following the return of left fielder Jayson Werth from the disabled list.[28] On September 7, the Nationals recalled Stevenson.[29] He finished the regular season with the Nationals, having appeared in 37 games, batting .158 with an RBI and a stolen base.[30]
2018
Stevenson began the 2018 season with the Triple–A Syracuse Chiefs, but the Nationals called him up to the major leagues on April 16.[31] Stevenson entered a game on April 25 against the San Francisco Giants at AT&T Park with only 10 major-league hits and two major-league RBIs in his career, but, playing in left field that day, he went 4-for-5 from the plate with two doubles and a walk and scored two runs as part of a Nationals offensive explosion that ended in a 15–2 Washington victory.[32] After Stevenson appeared in 25 games for Washington, hitting .255 with eight RBIs,[33] the Nationals optioned him back to Syracuse on June 1.[33]
2019
In 2019 he batted .367/.486/.467 in 30 at bats.[34]
2019 would also see him make his postseason debut: pinch-running for Ryan Zimmerman in the 8th inning of the Wild Card Game against the Milwaukee Brewers, he would score the tying run on Juan Soto’s single; acting aggressively due to Stevenson’s speed, Brewers right fielder Trent Grisham misplayed the ball, allowing the eventual winning run to score as well. While not on the playoff roster for the rest of the Nationals’ championship run, Stevenson would take the field before Game 3 of the World Series to catch the ceremonial first pitch from Apollo 11 astronaut Buzz Aldrin.
2020
In 2020 he batted .366/.447/.732 in 41 at bats.[34] He had the fastest home run trot of all major league players, at 17.3 seconds.[35]
2021
In 2021, Stevenson spent the majority of the year with Washington, also playing in 15 games for the Triple-A Rochester Red Wings. In 109 games for the Nationals, Stevenson slashed .229/.294/.339 with 5 home runs and 23 RBI.[36]
2022
On April 2, 2022, Stevenson was outrighted off of the 40-man roster.[37] He appeared in 135 games for the Triple-A Rochester Red Wings, slashing .279/.344/.457 with 16 home runs, 67 RBI, and 39 stolen bases. He elected free agency following the season on November 10.
Minnesota Twins
On March 9, 2023, Stevenson signed a minor league contract with the Minnesota Twins organization.[38] In 106 games for the Triple–A St. Paul Saints, he batted .317/.395/.522 with 16 home runs, 57 RBI, and 44 stolen bases. On September 1, Stevenson was selected to the major league roster after rosters expanded.[39] In 25 games for Minnesota, he hit .189/.250/.216 with no home runs, one RBI, and four stolen bases. Following the season on October 20, Stevenson was removed from the 40–man roster and sent outright to Triple–A St. Paul.[40] On October 23, Stevenson elected free agency.[41]
Stevenson was described by Nationals general manager Mike Rizzo after being drafted in 2015 as someone who "plays 100 mph with his hair on fire", a phrase he has also applied to standout players like Bryce Harper[43] and Adam Eaton.[44] He is considered to be one of the faster players in professional baseball, with highly rated defense in center field,[45] although baseball writer John Sickels in 2016 questioned his arm strength and ability to hit consistently.[46] He has a compact swing with great bat speed, but he is not considered a power hitter.[47]