The 6 ft 3 in (1.91 m) Lynn played at Celina High School and later at Texas Tech (1988–91), where he was an All-Southwest Conference running back in 1990. His senior year was cut short by a knee injury, and concerns about the injury left him undrafted. He was a journeyman reserve running back and special teams player during his NFL career, playing for the Denver Broncos (1993, 1997–99) and San Francisco 49ers (1995–96). He retired in 2000 due to repeated neck stinger injuries. Lynn was part of Denver's back-to-back Super Bowl champion teams (1997–98). In 1997 he had his best personal year as an NFL player.
Upon retiring in 2000, he joined the Denver coaching staff as an offensive assistant and special teams coach (2000–02), before joining the Jacksonville Jaguars as the running backs coach (2003–04). He left Jacksonville after being switched to special teams coach following a coaching staff shakeup by head coach Jack Del Rio in 2005 and quickly joined the Dallas Cowboys staff as the running backs coach. On January 26, 2007, with the retirement of Bill Parcells as Dallas head coach, Lynn signed on with the Cleveland Browns to fill their RB coach vacancy.
His son, D'Anton, played college football for the Penn State Nittany Lions, and was signed as an undrafted rookie by the New York Jets following the 2012 NFL Draft. During Cowboys training camp in 2005, Lynn was a victim of a hit-and-run automobile accident, suffering a broken nose and multiple lacerations.