On September 29, 2015, McMillan signed as a free agent to a one-year contract in the ECHL with the Idaho Steelheads.[3]
In his fourth year in the DEL in the 2022–23 season, McMillan helped Frankfurt in their first season in the top tier by recording 5 goals and 17 points through 55 regular season games. Following their defeat in the playoff qualifiers to Düsseldorfer EG, McMillan left Löwen Frankfurt at the conclusion of his contract on March 19, 2023.[4]
On July 6, 2023, McMillan returned to the DEL2, signing a one-year contract with the Kassel Huskies.[5]