He played in Major League Baseball (MLB) for the San Diego Padres, Miami Marlins, Houston Astros, Los Angeles Angels of Anaheim, New York Yankees, Pittsburgh Pirates, Seattle Mariners, Baltimore Orioles and St. Louis Cardinals and in Nippon Professional Baseball (NPB) for the Saitama Seibu Lions.

LeBlanc was drafted by the Tampa Bay Devil Rays in the 36th round of the 2003 Major League Baseball draft out of Alfred M. Barbe High School, but instead decided to attend the University of Alabama, where he played college baseball for the Alabama Crimson Tide.

In 2004, LeBlanc was named the Baseball America Freshman of the Year, becoming only the sixth SEC player and first pitcher since 1995 to win the award.

He posted a 5–1 record and a 3.02 ERA in 14 games, 10 starts, from Short-Season Eugene Emeralds and the Class-A Fort Wayne Wizards in 2006.

On June 29 against the Vancouver Canadians he earned his first win in his professional debut, tossing one scoreless inning of relief.

He made his Major League debut on September 3, but struggled, allowing four runs on eight hits with one strikeout in four innings.

He picked up his first Major League win on September 15 against the Colorado Rockies, yielding four runs over six innings with six strikeouts.

On June 30, 2012, LeBlanc was called up by the Marlins to replace Edward Mujica, who was placed on the disabled list with a fractured toe.

LeBlanc began 2013 as the fourth member of the Marlins rotation, where he made 7 starts before being moved to the bullpen in favor of Tom Koehler.

[14] He made one appearance with the Yankees, pitching an inning of relief on June 4, giving up 2 runs on 2 hits and a walk.

On December 17, 2015, LeBlanc signed a minor league contract with the Toronto Blue Jays that included an invitation to spring training.

[20] On June 22, 2016, LeBlanc was traded to the Seattle Mariners in exchange for cash considerations or a player to be named later.

LeBlanc was traded to the Pittsburgh Pirates in exchange for cash considerations or a player to be named later on September 13, 2016.

[22] The Pirates avoided going to salary arbitration with LeBlanc on December 3, 2016, by signing him to a one-year, $800,000 contract for the 2017 season with a $1.25 million option for 2018.

[30] LeBlanc pitched most of the season in the rotation, collecting 9 wins with a career low 3.72 ERA in 32 games, 27 starts.

He began the 2019 season as the Mariners 5th starter; after 3 starts he was placed on the disabled list with a grade 2 oblique strain, sidelining him 4–6 weeks.

[37] On May 4, 2021, LeBlanc signed a minor league contract with the Milwaukee Brewers organization and was assigned to the Triple-A Nashville Sounds.

[38] LeBlanc hurled 16.2 innings of 3.78 ERA ball in Nashville before exercising his opt-out clause and electing free agency on May 27.

[39] On June 1, 2021, LeBlanc signed a minor league contract with the Texas Rangers organization and was assigned to the Triple-A Round Rock Express.

On June 17, 2021, LeBlanc signed a major league contract with the St. Louis Cardinals and was added to the active roster.