Seattle Mariners The
Seattle Mariners selected Leone in the 16th round of the
2012 Major League Baseball draft, and he received a $100,000
signing bonus when he signed with the team. In July, Leone was promoted to the
Double-A Jackson Generals, where he ended the 2013 season. In 48 combined appearances across three minor league levels, Leone posted a 1–3 record, 2.25 ERA, and 64 strikeouts in 64 innings. He remained with the Mariners for the entire 2014 season, making 57 relief appearances and posting an 8–2 record, 2.17 ERA, and 70 strikeouts in 66 innings. During spring training in 2015, Leone struggled with his
command, and the Mariners assigned him to Triple-A Tacoma. When the Mariners placed
Tom Wilhelmsen on the disabled list in early April, they promoted Leone. Leone made 10 appearances with the Mariners in 2015, posting a 6.35 ERA and nine walks in 11 innings. Leone made three appearances for the Diamondbacks in 2015, and went 0–1 with a 14.73 ERA in 3 innings.
Toronto Blue Jays On November 18, 2016, Leone was claimed off waivers by the
Toronto Blue Jays. Though initially sent by the Blue Jays to their minor league camp late in spring training, Leone was recalled on April 2 to start the
2017 season with the major league club, taking the roster spot of the injured closer
Roberto Osuna. He was optioned to the Triple-A
Buffalo Bisons on May 30 but was recalled again on June 6. Leone was placed on the
bereavement list for undisclosed reasons on August 13, and activated on August 16. On September 11, Leone earned his first major league
save when he pitched a scoreless 9th inning in a 4–3 victory against the
Baltimore Orioles. Leone would finish his first season as a Blue Jay appearing in 65 games, posting a 2.56 ERA, and striking out 81 batters over 70 innings.
St. Louis Cardinals On January 19, 2018, the Blue Jays traded Leone and
Conner Greene to the
St. Louis Cardinals for outfielder
Randal Grichuk. On May 9, he was placed on the 10-day
disabled list with nerve damage in his right arm, and on May 30, he was transferred to the 60-day disabled list. In 13 innings pitched prior to his injury, he compiled a 4.15 ERA with 15 strikeouts. He was activated from the disabled list on August 26. Leone finished his first season in St. Louis with a 1–2 record and a 4.50 ERA in 29 relief appearances. Leone began 2019 in St. Louis' bullpen, but was sent down to the
Memphis Redbirds in May after pitching to an 8.02 ERA in innings. He was recalled to St. Louis on June 25, but optioned again on July 21. He was recalled once again on August 22, finishing the season in St. Louis. Over relief innings pitched during the regular season with the Cardinals, Leone went 1–0 with a 5.53 ERA, striking out 46. Leone was designated for assignment on November 20, 2019. He was released on November 25.
Cleveland Indians On January 23, 2020, Leone signed a minor league deal with the
Cleveland Indians. The Indians selected his contract on July 23. Leone was designated for assignment by the Indians on September 11. He had an 8.38 ERA over 9.2 innings pitched in 12 games for the Indians. After clearing waivers, Leone was outrighted to the Indians' alternate training site roster on September 13. He elected free agency on October 14.
San Francisco Giants On December 8, 2020, Leone signed a minor league contract with the
San Francisco Giants organization. On June 1, 2021, he was selected to the active roster. On October 3, Leone struck out
Eric Hosmer of the
San Diego Padres to end the last game of the season and clinch the
National League West division championship for the Giants. In 2021, Leone was 4–5 with 2 saves and a career-best 1.51 ERA. He pitched in 57 games (4 starts), covering innings in which he allowed 6.2
hits per nine innings. Leone was released by the organization on March 24. Leone re-signed with the Rangers on a new minor league contract on March 29. He made 8 appearances for the Triple-A
Round Rock Express, working to a pristine 1.59 ERA and 2–0 record with 15 strikeouts and 2 saves in innings pitched. On May 2, Leone opted out of his minor league contract and became a free agent.
New York Mets On May 4, 2023, Leone signed a one-year, major league contract with the
New York Mets. Hours after signing with the Mets, Leone's first game back was against the
Detroit Tigers where he pitched in relief for one inning. He faced three batters and had one strikeout.
Los Angeles Angels On August 1, 2023, Leone was traded to the
Los Angeles Angels in exchange for
Jeremiah Jackson. After posting a 5.54 ERA in 11 relief appearances, Leone was placed on waivers by the Angels on August 29.
Seattle Mariners (second stint) On August 31, 2023, Leone was claimed off waivers by the
Seattle Mariners. In 9 appearances for the Mariners, he registered a 4.35 ERA with 10 strikeouts across innings of work.
Chicago White Sox On February 13, 2024, Leone signed a minor league contract with the
Chicago White Sox. On March 27, the White Sox selected Leone's contract after he made the team's Opening Day roster. After struggling to a 7.04 ERA in 18 games, he was placed on the injured list with right elbow inflammation on May 24. Leone was transferred to the 60–day injured list on June 11. He was activated on August 5. After five more games for Chicago, Leone was placed back on the 60-day injured list with a
UCL sprain on August 16, ending his season. On October 26, 2024, Leone announced his retirement from professional baseball via
Instagram. ==Personal life==