McMillan lettered 4 times on the football field and 2 times on the diamond for the San Joaquin Memorial Panthers. Over his football career, he totaled 260 receptions for 5,234 yards and 54 touchdowns in 50 career games. He was named to the Cal-Hi Sports' all-state first team after his senior season. He was a consensus 4-star recruit who was ranked as the nation's No. 8 wide receiver by 247Sports. He committed to Washington over offers from Notre Dame and Alabama.
He played in 3 of the 4 games during the 2020 Covid-19 season and had 1 catch for 16 yards and 2 carries for 14 yards. In 2021 he played 11 games, starting 9 and put up solid numbers for the Huskies, collecting 39 receptions for 470 yards and 3 touchdowns.
Last season, McMillan helped welcome transfer quarterback Michael Penix to Washington by catching 79 passes for 1,098 yards and 9 touchdowns.
This season, McMillan has 45 catches for 559 yards and 5 touchdowns. He injured his leg September 16th against Michigan State and only has played sporadically for several games after. He finished the season well as he recovered from the injury.