Ryan, 67, had said before the season that he was planning to retire at the end of the 2015-2016 season.
“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 by the school after the game.
Long-time assistant Greg Gard is taking over as the interim coach at Wisconsin, which improved to a modest 7-5 with the win Tuesday night.
In 32 seasons at three stops, including Wisconsin-Platteville and Wisconsin-Milwaukee, Ryan had a career record of 747-233, including a 364-130 mark in 15 seasons at Wisconsin, with Final Four appearances at the end of each of the past two seasons.
Ryan had replaced Dick Bennett, the father of Virginia basketball coach Tony Bennett, after the elder Bennett had led the Badgers to a Final Four appearance in 2000.
Dick Bennett stepped down three games into the 2000-2001 season and was replaced on an interim basis by Brad Soderberg, who led the Badgers to an NCAA Tournament appearance, but was not given the job full time.
Soderberg is now on the staff of Tony Bennett at Virginia.