Donovan was born and raised in Rockville Centre on Long Island, New York, where he played basketball at St. Agnes Cathedral High School.

Donovan ended his professional basketball career in 1989 and briefly worked as a Wall Street stock broker before following Pitino to his new job at the University of Kentucky.

In June 2007, after leading the Gators to their second consecutive national title, he accepted an offer to become the head coach of the NBA's Orlando Magic.

In his first season with the team, the Thunder were division winners and reached the Conference finals, where they lost to the Golden State Warriors in seven games after building a 3–1 series lead.

[5] Billy Donovan Jr. attended St. Agnes Cathedral High School in Rockville Centre, where he played basketball under coach Frank Morris.

[6] With Donovan starting at point guard, St. Agnes won the Long Island Catholic High School Championship during his senior year.

Pitino scheduled introductory meetings with the players, during which Donovan informed him that he wanted to transfer to Fairfield or Northeastern, both smaller schools where he might get more playing time.

During his senior year, he averaged over 20 points and 7 assists per game and led the sixth-seeded Friars to the 1987 Final Four, while earning Southeast Regional Most Valuable Player honors.

[17] Pitino was tasked with rebuilding a Kentucky basketball program which had been devastated by sanctions levied by the NCAA due to earlier rules violations.

In that position, Donovan served as Pitino's top assistant during Kentucky's 1993 Final Four run, and he helped to recruit the members of UK's 1996 national championship team.

[7] Donovan's association with Kentucky's success plus Pitino's recommendation earned him an offer to become the head basketball coach at Marshall University, where the Thundering Herd had struggled to a 9–18 record during the 1993–94 season.

Donovan was also successful on the recruiting trail, convincing nationally sought prep star Jason Williams to decline scholarship offers from more established programs and remain in state to attend Marshall.

The Florida basketball program had only fleeting success over its history, and although the Gators reached their first Final Four under Kruger in 1994, his teams slipped back to mediocre levels.

Florida athletic director Jeremy Foley sought a "young, energetic, and enthusiastic" coach to bring sustained success, and after a wide-ranging search, he decided that 30-year-old Billy Donovan was the best fit.

While successful during the regular season, Donovan's Florida squads from 2001 to 2005 consistently underperformed in the NCAA tournament, losing to lower-seeded teams in the first or second round every year despite rosters stocked with highly recruited players.

Still in his thirties, some commentators speculated that Donovan was an excellent recruiter who was unable to make in-game adjustments or develop talented players once they were on the UF campus.

This loss was followed by a surprising season sweep at the hands of the eventual 2006 National Invitation Tournament champion South Carolina Gamecocks as Florida posted a 10–6 conference record, good for second place in the SEC Eastern Division.

During a post-championship celebration in the O'Connell Center, the Gators' entire starting five of (Lee Humphrey, Joakim Noah, Al Horford, Corey Brewer, and Taurean Green) announced they would return the following year and attempt to win another championship (the last back-to-back title winner was 1991 and 1992 Duke) instead of declaring early for the NBA draft.

On December 20, 2006, Donovan became the winningest basketball coach in Florida history, earning his 236th win to surpass Norm Sloan's total.

Florida earned the number one overall seed in the 2007 NCAA tournament and defeated Jackson State, Purdue, Butler and Oregon to reach the Final Four.

[28] However, after an 18–3 start, the team struggled during the final third of the season, winning just three of its last eleven games and snapping the Gators' nine-year streak of NCAA tournament invitations.

Donovan's 2013–14 squad started the year with several players injured or suspended and faced one of the most challenging non-conference schedules in college basketball.

On February 28, 2015, Donovan became the second youngest coach in NCAA Division I history to earn 500 career wins, accomplishing the feat in the Florida Gators' 66–49 victory over the Tennessee Volunteers.

"[32] After winning the 2007 national championship, Donovan announced that he had no plans to leave Florida for another college job and was working on a contract extension with UF.

However, in late May, the NBA's Orlando Magic offered Donovan their head coaching job to replace Brian Hill, who had been fired after two consecutive losing seasons.

Donovan struggled with the decision until June 1, 2007, when he agreed to accept the Orlando Magic's contract offer, reportedly worth $27.5 million over five years.

The next morning Donovan began having second thoughts about his decision, and informed Jeremy Foley and the Magic front office that he had changed his mind about leaving Florida.

[36][37] Donovan issued apologies to all involved parties, and the Orlando Magic soon after hired Stan Van Gundy as their head coach.

[47] Some commentators have opined that Donovan should have succeeded Mike Krzyzewski as the head coach of the United States men's national basketball team at the 2020 Summer Olympics.

[15] Similar tragedies struck the families of Pitino and former assistant coaches Anthony Grant and John Pelphrey, forging a closer bond between them.