Theus played his college basketball at UNLV for head coach Jerry Tarkanian from 1976 to 1978. In three seasons with the Runnin' Rebels, he (Reggie) averaged 12.9 points, 4.4 assists and 4.3 rebounds per game. Theus, who became one of the best players to ever don a UNLV uniform, shot 81 percent from the free-throw line for his career while amassing 1,177 career points (21st on all-time scoring list), 401 career assists and 389 career rebounds in just 91 collegiate games.
As a sophomore, Theus helped lead UNLV into the national spotlight as the Rebels went 29–3, advancing to the school's first Final Four in Atlanta, Georgia. Despite losing by a single point to University of North Carolina in the semifinals, UNLV defeated UNC-Charlotte in the third-place game and set NCAA single-season records for most points in a season (3,426), most 100-point games (23) and most consecutive 100-point games (12). He averaged 14.5 points, 4.5 rebounds and 4.3 assists per game while shooting 81.8 percent from the charity stripe and 49.7 percent from the field as a sophomore.
As a junior, Reggie was named a second team All-American after averaging 18.9 points, 6.8 rebounds and 4.5 assists per game.
In 1989, Theus was inducted into the UNLV Athletic Hall of Fame and in 1997 he became one of only six players in school history to have his jersey retired by the Rebels.
Theus has twice applied for the UNLV Runnin' Rebels coaching job to no avail. It is widely believed that he covets the head coaching job at his alma mater.
After attending UNLV and having a successful college career, Theus was selected by the Chicago Bulls with the 9th pick of the 1978 NBA Draft. A 6'7" guard, Theus averaged 16.3 points per game during his first season and was the runner-up for the 1979NBA Rookie of the Year Award. He garnered the nickname "Rush Street Reggie" while playing in Chicago for owning an apartment on that street and having an active social life around that area, being frequently spotted at the city night spots. He followed his stellar rookie campaign with a strong sophomore season, in which he averaged 20.2 points and 6.3 assists for the Bulls. In 1981, Theus appeared in his first All-Star Game; he appeared again in 1983, during a season in which he averaged a career high 23.8 points per game.
Inexplicably, however, newly hired Bulls coach Kevin Loughery decided to bench Theus for the first half of the 1983–1984 season, and Theus was soon traded to the Kansas City Kings for Steve Johnson and three draft picks, a move that saddened many Chicago fans who enjoyed Theus' enthusiasm and energy. Theus continued his impressive play during his tenure with the Sacramento Kings, averaging at least 18 points per game in each full season he played for them. Theus is one of only two players in league history listed at 6 ft 6 or taller to tally more than 750 assists in an NBA season (788 in 1985–86), the other player is NBA legend Magic Johnson.
In 2005, Reggie Theus was hired by the New Mexico State Aggies as the head coach of the men's basketball team after the retirement of head coach Lou Henson. In his first season, Theus turned the Aggies from a 6–24 squad in 2004–05 to a 16–14 team in the 2005–06 season – matching the fifth best turn-around for a Division-I men's basketball team. Reggie Theus is currently the head coach of California State University Northridge. In his first season with the Matadors he led them to a 17-18 record, but managed to reach the Big West Finals where they lost to Cal Poly San Luis Obispo.
In his second year as head coach, Theus led NMSU to their 17th NCAA tournament, their first tournament appearance since 1999, and coached NMSU to its 14th conference tournament title which earned them an automatic bid into the NCAA tournament.
On June 19, 2007, Theus was hired by the Maloof brothers and guaranteed three years as head coach of the Sacramento Kings. He noted his hiring as coach had brought his career to "full circle", as he once played in the NBA with the Kings. Marvin Menzies succeeded him as head coach at New Mexico State.
On December 15, 2008, Theus was fired by the Kings and the team announced that their assistant coach Kenny Natt would lead the team in the interim period.
National champion Postseason invitational champion Conference regular season champion Conference regular season and conference tournament champion Division regular season champion Division regular season and conference tournament champion Conference tournament champion