Mannering, a right-handed pitcher from Smyrna, Delaware, spent four collegiate seasons at the University of Pittsburgh at Bradford, where he developed into a reliable arm on the mound. Over his career, he recorded 11 wins and four saves while striking out 186 batters across 172.2 innings pitched, finishing with a 5.26 ERA. During his senior season, he posted a 2.70 ERA with 62 strikeouts and just 12 walks, earning Second Team All-AMCC honors after being named a First Team selection as a junior. 

After graduating in 2025, he began his professional career with the Milwaukee Milkmen of the American Association, where he appeared in six games and posted a 2.35 ERA over 7.2 innings pitched.