After his baseball playing days at NIU as a 5-9, 165-pound infielder, O'Neill has gone on to become a very successful NCAA Division I men's basketball official, starting that career in 1977. Since then, O'Neill has worked in every major conference across the U.S. except the ACC, spending 25 years in the Big 12, 22 years in the Big Ten, 15 years in the Southeastern Conference, and two years in each of the Big East and Pacific 10 conferences. He has also officiated in every season of the Conference USA's existence (15 years) and has worked several years in the Atlantic 10, Mid-American, Mountain West and Western Athletic conferences. O'Neill has worked 100 games in each of the last seven years and officiated in the NCAA Tournament 24 times (71 games), a mark reached by only a handful of officials. His NCAA Tournament portfolio is highlighted by four Final Fours [1991: Duke vs. UNLV, 1997: Kentucky vs. Arizona (National Championship), 2007: Florida vs. UCLA, 2009: MSU vs. UNC (National Championship)]. O'Neill also worked the first College Basketball Invitational championship game in 2008 between Tulsa and Bradley. O'Neill officiated milestone wins for legendary coaches Homer Drew (700th), Denny Crum (600th), Jim Boeheim (500th) and Bob Knight (500th). Along the way, O'Neill has officiated games with some of the best players the game of basketball has ever seen, including Michael Jordan, Larry Bird, and Patrick Ewing.
Playing baseball at NIU and refereeing basketball games runs in the O'Neill family as his two sons, Rick and Tom Jr., are also Division I officials, while his other son, Michael, is a D-II and D-III official, aspiring to reach D-I. Michael (1995-98) and Tom Jr. (1992) also wore Huskie baseball uniforms as infielders. On November 30, 2001, three of the O'Neill's became the first family trio to officiate an NCAA basketball game as Tom, Tom Jr. and Rick O'Neill all worked the contest in Milwaukee, Wis. between host Marquette and Houston Baptist.
Aside from his career in the NCAA, O'Neill had a brief stint in the NBA, working the 1989-90 season before deciding to stay with the college game. Throughout his career, O'Neill has also been heavily involved with high school basketball in Illinois. In 2002, he was inducted into the Illinois Basketball Coaches Association Hall of Fame. O'Neill has been the supervisor of officials for the south-suburban Chicago area's South Inter-Athletic Association Conference for 25 years. Additionally, O'Neill has the longest running basketball officiating camp, "The Tom O'Neill Officiating Camp," that will be run for the 24th time this year. O'Neill has also impacted the Chicago area softball scene as he was inducted into the Chicago 16 Inch Softball Hall of Fame in 2000. That same year, he became vice-president of the Amateur Softball Association, where he served as one of 101 commissioners throughout the U.S. since 1985. O'Neill was the director of the Blue Island Softball League for 22 years. From 1980-89, all ASA major championships were won by Blue Island teams.
In his days of competition, O'Neill played baseball and basketball at Eisenhower H.S. before becoming a Huskie. In 1966, he played in four games as an infielder for NIU, picking up a hit and run scored, for a team that went 13-6-1 and recorded a second-place finish in the Interstate Intercollegiate Athletic Conference with a 6-2 mark. O'Neill worked in the Sports Information Office at NIU during the fall and winter of 1966-67 as a statistician under Bud Nangle. In 1967, O'Neill played in all 35 games at second base for NIU and led the team in walks (33) for a 20-14-1 squad. In 1968, he hit .287, led NIU in walks (23) and ranked second in doubles (6) and runs scored (19) for a 13-14-1 team. While at Northern, he majored in physical education and journalism.
