Mitchell was drafted in the 4th round of the 1969 NFL draft by the Atlanta Falcons, who made him the 81st pick of the draft. During his rookie season the big tight end caught 22 passes for 339 yards, scoring 4 touchdowns — sufficient to win him a place on the 1969 Pro Bowl team.[3]
He nearly doubled his production during his second season with the team, catching 44 balls for 650 yards and 6 touchdowns.[2] Although the Falcons were a poor team in these years, Mitchell emerged as an offensive star and team leader and he was named captain of the Falcons offense in 1971.[2]
Mitchell was again named to the NFL Pro Bowl team in 1972.[2]