Harrington led the Texas State baseball team to its first Sun Belt Conference championship in 2019.
"I chaired the search committee when Ty was hired 20 years ago," Teis said in a Texas State press release. "Ty mentioned to me six weeks ago that he has been a head coach all his life and wanted to try something new. I tried to talk him out of retirement then and did so up until the end. He has been a great ambassador for Texas State, and not just the athletics department, but the university as well. It will be very different in the dugout at Bobcat Ball Park. We wish him, Leila, and the girls the best as they enter life without baseball in their future."
Harrington, who was hired in 2000, will leave the university's baseball program as its all-time winningest coach, the press release stated.
"This has been an incredible 20-year journey filled with inspiring players and people, great teams, memorable wins, a university that is a rising star, loyal fans and an incredible community," Harrington said in the release. "Most of all, I have lasting personal relationships that I will cherish forever. Each player and team has had a significant impact, made an impression and enriched my life. I hope in some form or fashion that I have had some positive impact on their lives."