After graduation from high school, Tiller enrolled at the Montana State University and played offensive line for the Bobcats, starting for three seasons.

After helping the Bobcats to three consecutive Big Sky championships in 1966, 1967, and 1968, he reunited with Sweeney when he became the line coach and offensive coordinator for the Washington State.

Tiller then became and assistant with the Calgary Stampeders, eventually serving as the interim head coach in 1976, where he led the team to their only two wins of that season.

[2] Upon his high school graduation, he attended Montana State University in Bozeman, where he played football for the Bobcats under head coaches Herb Agocs and Jim Sweeney, and was a member of Delta Sigma Phi fraternity.

[4] Tiller was selected in the 1964 AFL draft by the Boston Patriots;[5] he was the 140th pick overall (18th round) but chose to sign with the Calgary Stampeders of the Canadian Football League.

[2] The following year, he was promoted to full-time assistant coach, working with offensive and defensive lineman, as well as an instructor in physical education.

Guided by junior quarterback Jim Everett, the 1984 team became the first in school history to defeat Notre Dame, Michigan, and Ohio State in the same season.

As offensive coordinator in 1989 at Washington State under head coach Mike Price, he helped RB Steve Broussard to 1,237 yards with 13 TD.

His best team was his final season in 1996, which notched a 10–2 record (7–1 in WAC play winning the Pacific Division[9]), but was left out of a bowl after losing to BYU in the inaugural WAC Championship game—to date, the last team to finish ranked in a major poll and not receive a bowl invitation while eligible.

Prior to Tiller's tenure as head coach, Purdue had played in only five bowl games, most recently in 1984 when he was the defensive coordinator.

In 2008 against Central Michigan, Tiller won his 85th game at Purdue to become the winningest coach in school history, topping the previous mark set by Jack Mollenkopf (1956–1969).

[11] Tiller's "basketball on grass" offense, originated by legendary high school coach Jack Neumeier, and learned from Tiller's coaching colleagues Jack Elway and Dennis Erickson, was well renowned for its ability to score and score effectively, befuddling opposing defenses.