Gagliardi, who turned 86 on Nov. 1, said he was stepping down after 70 years as a head coach.
He started as a player-coach on his high school team at the age of 16 after the regular coach was called into military service in World War II.
Gagliardi was a high school coach for six years before coaching Carroll College in Montana for four seasons. He took over the program at St. John's (Minn.) in 1953 and has been at the Collegeville, Minn., school since.
"Seventy years is a long time to be doing the same job," Gagliardi said. "Luckily, I've always been blessed with great players, friends, family and support to make it this far.
"Nobody ever said that getting older was easy. I just can't do the job at the level I used to anymore."
Gagliardi amassed a record of 489-138-11 at Carroll and St. John's. His win total is the highest among all levels of college coaches. His record at St. John's is 465-132-10.
He helped St. John's to NAIA championships in 1963 and 1965 and won NCAA Division III titles in 1976 and 2003.
The Johnnies were 5-5 this season, the first season Gagliardi didn't win more than he lost since 1986. He had just two losing seasons -- both 3-4 records -- in his collegiate career.