Kelso played in eight NFL seasons and his entire career with the Buffalo Bills from 1986-1993. His peak performance as a pro came during the 1988 season when he had intercepted 7 passes for 180 yards and one touchdown. Kelso appeared in four consecutive Super Bowl appearances for the Bills from 1990 to 1993. He was well known for wearing a "pro cap" on his helmet which was used to reduce the risk of concussions. He finished his career with 30 interceptions, 8 fumble recoveries, and two defensive touchdowns.
Starting with the 2006 NFL season, Kelso has served as the color commentator for Buffalo Bills radio broadcasts on WGRF 96.9 FM and currently WGR 550. He is the Development Director (since 2003-2004) at Saint Mary's High School in Lancaster, New York, as well as its varsity football defensive coordinator from the 2003-2010 seasons. Kelso also is a local baseball coach. Prior to that he taught fifth grade at Main Street Elementary School.