Bo Ryan announced his retirement, effective immediately, following Wisconsin's win over Texas A&M-Corpus Christi on Tuesday.
"After months of conversation with Barry Alvarez and his administrative staff, as well as my wife, Kelly, I have decided that now is the right time to step down from the head coaching position here at Wisconsin," Ryan said in a statement released after the game.
Ryan led Wisconsin to the National Championship Game last season.
Ryan, who turns 68 on Sunday, had said in a statement in June that he would coach this season and then step down.
Greg Gard will take over as interim head coach.
"This was a decision months in the making," Ryan said. "I brought this up to Barry back in April. He advised me to take some time to think it over, and I appreciated that. But in recent weeks, I have come to the conclusion that now is the right time for me to retire and for Greg Gard to have the opportunity to coach the team for the remainder of the season. I discussed this with Barry, and I appreciate him giving me the space to make this decision."