[1] Leclerc made his professional debut in 2011 with the DSL Rangers, posting a 3–1 win–loss record with a 2.36 earned run average (ERA) and 27 strikeouts in 34+1⁄3 innings pitched.

He returned to the DSL Rangers for the 2012 season, pitching to a 3–1 record, a 1.54 ERA, and 41 strikeouts in 46+2⁄3 innings.

Leclerc was utilized as a starting pitcher for the Frisco RoughRiders of the Double-A Texas League in 2015.

He received a midseason promotion to the Round Rock Express of the Triple-A Pacific Coast League, where he posted a 2–2 record with a 2.72 ERA and 50 strikeouts in 43 innings.

[4] In all, Leclerc posted a 0–0 record with a 1.80 ERA, 15 strikeouts, and 13 walks in 15 innings (12 games) of major league action.

Leclerc was named the 2018 Rangers' Pitcher of the Year by the Dallas-Fort Worth chapter of the Baseball Writers' Association of America.

On March 29, 2021, it was announced that Leclerc would undergo Tommy John surgery and miss the 2021 season.

[13] Leclerc appeared in 57 games for the Rangers in 2023, posting a 2.68 ERA with 67 strikeouts across 57 innings pitched.