The New York Mets selected him in the 48th round of the 2009 Major League Baseball draft.

He started the season with the West Michigan Whitecaps and was later promoted to the Double-A Erie SeaWolves.

[14] Mantiply spent the 2017 season with the Triple–A Scranton/Wilkes-Barre RailRiders, making 35 appearances and registering a 6–5 record and 2.83 ERA with 62 strikeouts across 70 innings pitched.

[15] On November 13, 2017, Mantiply signed a minor league contract with the Cincinnati Reds.

[16] On March 9, 2018, Mantiply underwent Tommy John surgery, and was ruled out for entirety of the season.

He earned his first major league win after relieving Chad Green for three innings.

[22] With the 2020 Arizona Diamondbacks, Mantiply appeared in 4 games, compiling a 0–0 record with 15.43 ERA and 2 strikeouts in 2.1 innings pitched.