Runnells attended the University of Northern Colorado and originally signed with the San Francisco Giants.

Runnells began his managerial career with Cincinnati's AA Eastern League affiliate, the Vermont Reds, in 1987.

In 1989, his Indianapolis Indians won the American Association championship and the "AAA Classic", earning him a promotion to a coaching position with the parent Montreal Expos.

On June 2, 1991, he was promoted again to manager of the Expos, who were lodged in last place in the National League East Division after 49 games.

He was General Manager Dave Dombrowski's hand-picked man but failed to replicate his minor league success as the Expos finished the 1991 season in last place for the first time since 1976.