Reynolds was drafted by the New York Mets in the second round of the 2012 Major League Baseball draft. The Mets moved Reynolds to shortstop after he signed. He made his professional debut that season for the Savannah Sand Gnats of the A-level South Atlantic League, hitting.259 with 3 home runs in 42 games. In 2013, Reynolds played in 117 games for the High-A Florida State League, and one game for the Double-A Binghamton Mets. He hit a disappointing.225/.300/.335 with five home runs in 436 at bats. Reynolds started the 2014 season back with Binghamton and was promoted to the Triple-A Las Vegas 51s after hitting.355 in 58 games. With the 51s, he finished 2015 batting.267/.319/.402, with 65 RBIs and 6 home runs in 115 games. Reynolds spent the 2015 regular season in Triple-A before being called up to the Mets during the 2015 NLDS to replace the injured Rubén Tejada. In doing so, he became the first player in modern baseball history to be added to a postseason roster in the middle of a series without previous major-league experience. He also became the third player in modern baseball history to be included on a postseason roster without previous major-league experience, after Chet Trail and Mark Kiger. He was dropped from the roster for the World Series, and did not appear in any games in the playoffs. The Mets promoted Reynolds to the major leagues on May 17, 2016. He made his major league debut at third base for the Mets that night. He went 0-3 with one strikeout. On May 25, Reynolds picked up his first major league hit, a single, against Nationals' pitcher Tanner Roark. Reynolds was sent down to the 51s to make room for Wilmer Flores, who came off the disabled list. Reynolds appeared in eight games during his first big league stint. He had a.100 batting average. Reynolds was recalled again on June 3 after David Wright was placed on the disabled list. In a June 22 game, Reynolds started and appeared in the outfieldfor the first time in his professional career and also hit his first Major League home run, off of reliever Joakim Soria. For 2016, he batted.225/.266/.416. On December 12, 2016, he underwent a right wrist debridement at the Hospital for Special Surgery. On March 21, 2017, he was optioned to the Mets minor league camp, but he was recalled one month later. In 2017 with the Mets, he batted.230/326/.301 in 130 plate appearances. On February 7, 2018, Reynolds was designated for assignment.
Washington Nationals
Reynolds was traded to the Washington Nationals for cash considerations on February 12, 2018. He began the season with the Class AAA Syracuse Chiefs, but the Nationals called him up to the major leagues on April 7. He appeared in 10 games and batted 1-for-12 with a walk before the Nationals optioned him back to Syracuse on April 24. He was called up again to replace Anthony Rendon who was placed on the family medical leave list. The Nationals designated Reynolds for assignment on January 13, 2019, clearing a roster spot for newly signed second basemanBrian Dozier. He was outrighted on January 18, 2019. He became a free agent following the 2019 season.
Kansas City Royals
On November 16, 2019, Reynolds signed a minor league contract with the Kansas City Royals.
