Thibault had been the Sun's only coach, hired when the team relocated from Orlando before the 2003 season.
He led the Sun to the WNBA Finals in 2004 and 2005, and five Eastern Conference Finals. The Sun finished the 2012 season as the top seed in the East with a 25-9 record. Led by league MVP Tina Charles, the team swept New York in the first round of the playoffs before losing to eventual WBNA champion Indiana in three games in the conference finals.
"We have the ultimate respect and appreciation for everything coach Thibault has done here, and he has played a huge part in establishing the Connecticut Sun as the model franchise in the league," said Mitchell Etess, the Sun's chief executive officer. "However, our ultimate goal is the championship, and this change is made in with an eye to accomplishing just that."
Sun assistants Scott Hawk and Bernadette Mattox also were let go.
Thibault had a 206-134 regular-season record with the Sun and was named the WNBA Coach of the Year in 2006 and 2008. He needs just six more victories to pass former Houston Comets coach Van Chancellor for the most wins in WBA history.
Thibault, who came to the Sun after being an assistant coach with the Milwaukee Bucks, said he turned down an opportunity this summer to return the NBA because
He said he's disappointed not to be able to finish the job in Connecticut with a championship, something he felt the team was close to achieving.
"I think we were headed in the right direction," he said. "I think if you ask the players, they think we were headed in the right direction. But I'm not the one to set the direction anymore."
Thibault said he has not ruled out returning to the WNBA with another team, but wants to take his time to consider his options before making his next career move.
Sun officials said they would begin formally interviewing candidates for their coaching job immediately, but set timetable to name Thibault's replacement.
"We are committed to bringing a WNBA championship to our loyal fans, who have given us tremendous support our first 10 seasons," general manager Chris Sienko said. "We have several candidates in mind who we believe can help us accomplish that goal.
"Ultimately, we want to find the best fit for our athletes and this organization."