During his four year career, he shattered the stolen base record, almost doubling the previous player with 141. McMillan spent the winter of 1972 as a starter on the United States national baseball team that played in the World Tournament in Managua, Nicaragua. With that team, he batted .308 with 20 hits, 15 runs, five doubles and six stolen bases to help team USA take second place at the tournament. Additionally, he became the only American to be named to the All-World team.
After his career as a Dolphin, he was a second round selection of the Cleveland Indians. Soon thereafter, he became the first Dolphins to reach the Majors Leagues after breaking through with the Seattle Mariners for a brief stint in 1977.