Winslow grew up in E.St.Louis, and is a former star tight end football player with the University of Missouri and the San Diego Chargers.

He was drafted in the first round of the 1979 NFL draft by the Chargers and played for them until 1987, when he retired from football due to injury. Winslow is frequently credited, along with Ozzie Newsome and John Mackey, with redefining the position of tight end. Historically, tight ends were primarily blockers who also ran short pass routes. Winslow had the size to block and the speed to get downfield quickly along with great athletic ability to both make difficult catches and run well with the ball after the catch.

In the 1982 playoff game against the Miami Dolphins, Winslow caught 13 passes and blocked a field goal with seconds remaining to send the game to overtime in one of the greatest single player efforts in Chargers history. After the game Winslow was helped off the field by his fellow San Diego Chargers. Winslow played in five Pro Bowls, was elected to the Pro Football Hall of Fame in 1995, and the College Football Hall of Fame in 2002. In his 9 NFL seasons, Winslow caught 541 passes for 6,741 yards and 45 touchdowns. Kellen is also a member of the NFL's 75th Anniversary All-Time Team. 

Since his retirement, Winslow has worked as a college football announcer with Fox Sports Net.

Winslow's son, Kellen Winslow Jr., also plays tight end in the NFL. Coincidentally, Winslow Jr. was drafted in the first round of the 2004 NFL draft by the Cleveland Browns - the team the Chargers traded with to draft the elder Winslow in 1979. Kellen Winslow Jr. wears his father's number as a sign of respect for his accomplishments.

Winslow has served as the athletic director of Central State University.