New York Yankees

Smith was drafted by the New York Yankees in the 14th round of the 2013 Major League Baseball draft out of Sam Houston State University.^[3][4] He made his professional debut for the Staten Island Yankees and also started one game for the Trenton Thunder. He finished 1–2 with a 1.93 earned run average (ERA) and 57 strikeouts over 51+1⁄3 innings in 14 games (10 starts). He started 2014 with the Charleston RiverDogs. He was named the South Atlantic League player of the week on April 28 after setting a RiverDogs strikeout record with 13.^[5][6] He finished the season with the Tampa Yankees. In 27 starts between Charleston and Tampa, he pitched to a 10–9 record and 3.67 ERA. Smith spent 2015 with the Trenton Thunder where he was 10–7 with a 3.38 ERA in 25 games (24 starts) along with pitching one game for the Scranton/Wilkes-Barre RailRiders at the end of the season. In 2016, he returned to Trenton where he compiled a 3–5 record and 3.96 ERA in 63.2 innings pitched.^[7]

On December 8, 2016, Smith was selected by the Milwaukee Brewers in the 2016 Rule 5 draft and then traded to the Chicago Cubs.^[8][9]

The Cubs returned Smith to the Yankees on March 28, 2017.^[10] The Yankees promoted Smith to the major leagues on July 16.^[11]

Miami Marlins

On November 20, 2017, Smith was traded to the Miami Marlins along with Garrett Cooper in exchange for pitcher Mike King and international bonus pool money.^[12] Smith earned a spot in the Marlins' Opening Day starting rotation and was pitching effectively until he severely strained and tore his lat muscle from the bone during a game against the Rockies on June 26. He opted to have season-ending surgery which ended his 2018 campaign.^[13] He posted a 5–6 record as a rookie with a 4.19 ERA and 88 strikeouts in 77.1 innings pitched.

Smith earned a spot in the 2019 Opening Day rotation and had a stretch of six consecutive quality starts from April 7 through May 7. However, the Marlins placed him on the injured list with left hip inflammation after his outing on June 6.^[14] He was activated on July 6.

Overall in 2019, Smith was 10–11 with a 4.52 ERA. He established new career highs with 168 strikeouts and 28 starts. He also allowed 33 home runs, the second-highest total in a single season in Marlins history.^[15]

Arizona Diamondbacks

On August 31, 2020, Smith was traded from the Marlins alongside pitcher Humberto Mejía and Julio Frias to the Arizona Diamondbacks in a package deal for outfielder Starling Marte.^[16] Smith pitched in 4 games (3 starts), totaling 11 innings of work with 12 strikeouts.

On August 18, 2021, Smith was suspended for ten games by Major League Baseball for having a foreign substance in his glove.^[17] In 45 appearances (13 starts) for Arizona, Smith logged a 4–9 record and 4.83 ERA with 124 strikeouts in 113.2 innings pitched.

Smith pitched in 44 contests for the Diamondbacks in 2022, posting a 1–3 record and 4.11 ERA with 65 strikeouts in 70.0 innings of work. In the final day of the season, Smith left a game against the Los Angeles Dodgers with what was later diagnosed as a partial tear in the ulnar collateral ligament of his throwing arm.^[18] He was designated for assignment on November 15, 2022. On November 18, Smith was non–tendered by Arizona and became a free agent.^[19]

Pittsburgh Pirates

On February 9, 2023, Smith signed a minor league contract with the Pittsburgh Pirates organization.^[20] He underwent Tommy John surgery in June.^[21] He elected free agency on November 6. ^[22]