Harrah was a 1974 All-America selection by NEA and TSN, Time magazine as a tackle. He was a Second-team All-America pick by UPI and AP. Was a 6-5 259 senior who could run a 4.8 40-yard dash and bench press 500 pounds. He is a member of the University of Miami Sports Hall of Fame.
Selected 11th overall by the Los Angeles Rams in the 1975 Draft. He helped the Rams win the NFC West 6 times (1975–79 and 1985) and the 1979 NFC Championship. During his tenure with the team the Rams led the NFC in Points Scored in 1976, Total Yards Gained in 1980 and Yards Rushing in 1976 and 1980. Served as team captain for 6 years and played in the Pro Bowl 6 times.
As a rookie in 1975 he backed up starter Joe Scibelli and played on special teams. In 1976 he took over at right guard and held that position for 12 seasons.
Off the field, Harrah starred in the 1986 rap music video "Ram It," bragging that he "learned long ago if you ram it just right, so you can ram it all day and ram it all night. "