The Cleveland Browns selected Warfield with the 11th pick of the 1964 NFL Draft. There was some thought for Warfield to play as a defensive back. But during workouts prior to the season, his play as a wide receiver impressed head coach Blanton Collier, and he was converted to the position. In his rookie season, he caught 52 passes for 920 yards and nine touchdowns. He averaged 17.8 yards per reception, and his speed served to complement the power of star running back Jim Brown. The Browns finished the season atop the East Division with a 10–3–1 record, and defeated the Baltimore Colts 27–0 in the 1964 NFL Championship Game. Warfield was invited to his first Pro Bowl and was named a first-team All-Pro by the Newspaper Enterprise Association (NEA).