In 2019, an ESPN Blue Ribbon Panel selected Keeler as one of the 150 greatest coaches in college football history.
He became Rowan's head coach in the 1993 season, ending his tenure in 2001 with an 88–21–1 (.804) record and seven NCAA Division III playoff appearances.
After Raymond retired in 2002, Keeler was named the fourth Delaware Fightin' Blue Hens football coach in 62 years.
Under Keeler, Delaware won its first national championship since 1979 and its first-ever Division I-AA title (in 2003) with a 15–1 record and a 149–23 total score in the four-game playoff series.
The Wilmington News Journal reported that Keeler was forced to hire an agent after the 2003 championship to help manage speaking engagements, guest appearances and private functions.
Keeler's team won three playoff games, including a win over his old CAA rival Villanova, before losing in the semifinals.
Led by Walter Payton Award winner Jeremiah Briscoe, Sam Houston State won the Southland Conference and made an FCS playoffs run before being blown out by James Madison in the quarterfinals.
Keeler led the 2020 Bearkats to a 10–0 season, culminating with a 23–21 win over the South Dakota State Jackrabbits in the 2021 NCAA Division I Football Championship Game.
Keeler accepted the head coaching job at Temple University following the 2024 regular season, replacing Stan Drayton.