Connor Sullivan graduated from College Park High School in 2019, where he was a three-sport athlete in baseball, football, and soccer. As a starting pitcher, he was a two-time NCS All-League selection, earning First Team honors as a junior in 2018. In his senior season (2019), Connor logged 69.2 innings pitched with a 2.63 ERA and 1.36 WHIP across 14 games pitched and 11 starts.

Connor continued his athletic career at the College of San Mateo (2019-2021), playing both baseball and football while maintaining his role as a starting pitcher. As a true freshman in 2021, he pitched a team-high 42.1 innings and went 3-2 in seven starts. During his second year, he committed to the University of California, Berkeley.

At Cal, Connor played three years and logged 111 innings in various roles including starter, reliever, and closer. After graduating in 2024, he signed with the Oakland Ballers professional baseball team midway through their inaugural season, immediately making an impact with a 1.69 ERA over 21.1 innings.

Returning as the team's closer for the 2025 season, Connor helped lead the Ballers to a championship with a 73-23 record. In 42 appearances across 104 games, he broke the modern era MLB-partner save record and tied the all-time Pioneer League record with 19 saves.