Upon graduation from Boston College, O'Shea became a graduate assistant at Rhode Island for the 1984-85 season before returning to The Heights as a grad assistant at BC from 1985-86. After a two-year stint as an assistant at Yale, O'Shea returned to URI, joining Al Skinner's staff, where he stayed for nine seasons. While on the Rams staff, O'Shea was a part of two NCAA Tournament bids along with two NIT bids. He is credited with recruiting Cuttino Mobley among others to URI. O'Shea followed Skinner and returned to his alma mater once again after Skinner accepted the Boston College job in 1997. He remained on the staff until 2001, when he landed his first head coaching gig at Ohio, just a year after the Eagles won both the Big East regular season and tournament titles, finishing with a 27–5 record and earning three-seed in the NCAA Tournament.
Ohio
In his first season in charge of the Bobcats, O'Shea guided the team to a 17–11 record, including wins overDePaul and North Carolina. A year later, O'Shea and Ohio posted a 14–16 record, with the season highlighted by a victory over Virginia. Following the 2002–03 season, forwardBrandon Hunter became the first Bobcat selected in the NBA Draft since 1995 when the Boston Celtics selected him in the second round. A year later, after losing Hunter, sixth-man Sonny Johnson and three-point shooter Steve Esterkamp, the 2003–04 Bobcats slipped to a 10–20 record, but bounced back in 2004–05, posting a 21–11 record en route to the NCAA Tournament. The 2004–05 Bobcats captured significant non-conference victories against San Francisco, Butler and Detroit, then won 11 of their last 15 contests down the stretch. O'Shea won the MAC Tournament but their run ended in the first round of the NCAA Tournament against Florida, falling 67–62, overcoming a 20-point second-half deficit, but coming up just short. With expectations high in 2005–06, O'Shea and Ohio compiled 19 victories before falling to eventual league champion Kent State in the MAC Tournament semifinals. The Bobcats registered victories at Marist, Rhode Island and Toledo, against Akron and Samfordat home, and took 18th-ranked Kentucky to the wire in Cincinnati, Ohio. From 2003 until O'Shea's departure in 2008, Ohio would have five-straight winning seasons with at least 19 wins each season. O'Shea was 120–95 in eight seasons in charge.
Bryant
O'Shea returned to his New England roots when he signed an eight-year contract to take over the head coaching duties at Bryant as the school transitioned to a full Division I member of the Northeast Conference. The Bulldogs broke through in the Bulldogs' first season of full Division I eligibility in 2012-13, winning 19 games and hosting a game in the College Basketball Invitational. Bryant went 16-15 the following season with an NEC semifinal appearance, but the Bulldogs failed to make the NEC Tournament in two of O'Shea's final three seasons at the helm, including an injury-plagued 2017-18 campaign in which Bryant's four leading scorers made a total of four starts together, all in the month of November. On February 12, 2018, O'Shea announced his retirement from Bryant, effectively at the end of the 2017–18 season.
