McMillan earned immediate playing time his true freshman year at Arizona in
2022. In his collegiate debut, he had three receptions for 53 yards and a touchdown in the 38–20 victory over
San Diego State. On October 15 against
Washington, he had seven catches for 132 yards and two touchdowns in the 49–39 loss. McMillan finished the season leading all true freshmen nationally with 702 receiving yards and eight touchdowns on 39 receptions. In
2023, McMillan had a breakout season with 90 receptions for 1,402 yards (fifth-most in the nation) and ten touchdowns over 13 games. He caught two touchdowns in a 31–24 loss to No. 7
Washington and followed with a 141-yard performance against No. 9
USC. In a 42–18 win over No. 22
Utah, McMillan had 116 receiving yards, a touchdown, and threw his first career touchdown pass. Against
Arizona State, he caught 11 passes for 266 yards and two touchdowns, setting a new
Territorial Cup receiving yards record as the Wildcats won 59–23. He was named a third-team AP
All-American at the end of the regular season. In the
2023 Alamo Bowl against No. 12
Oklahoma, McMillan had ten receptions for 160 yards for Arizona as they won 38–24, finishing the season on a seven-game winning streak. After head coach
Jedd Fisch left Arizona to take the
Washington head coaching job, McMillan elected to remain at Arizona for the
2024 season. Prior to the season, McMillan was named a preseason first-team AP All-American and was a projected first-round pick in the
2025 NFL draft. In the Wildcats' opening game of the 2024 season against
New Mexico, McMillan caught ten passes for a school-record 304 yards and tied the school record with four touchdown catches in a 61–39 victory. Two weeks later, he posted a career-high 11 receptions for 138 yards in a loss to No. 14
Kansas State. In a loss to
West Virginia, he finished with ten receptions for 202 yards and a touchdown. He finished the season third in the nation with 1,319 yards on 84 receptions and was named a
2024 Consensus All-American. He was also a finalist for the
Fred Biletnikoff Award, losing to
Travis Hunter. Following his junior season, McMillan declared for the 2025 NFL draft, finishing his college career with 213 receptions, 3,423 receiving yards, and 26 touchdowns in three seasons. His 3,423 yards are the most in
Wildcats program history, and his receptions and touchdowns rank in the top five in school history. ==Professional career==