He played college basketball for the Bowling Green Falcons where he was named to multiple All-Mid-American Conference teams.

The result was averages of 14.7 points, 8.0 rebounds and 2.7 blocks per game as a senior and shooting percentages of 56.3% on field goals and 41.9% on three-pointers.

[16] On October 8, 2017, Holmes was ruled out for approximately three weeks after being diagnosed with a non-displaced fracture in the radial bone of his left wrist.

[20] Holmes later recorded a new season high of 19 points in a 123–119 overtime loss to the Los Angeles Clippers on December 10.

[21] Holmes also recorded a double-double of 12 points and a new season high of 11 rebounds on March 15, 2019, during only 16 minutes of play in a 108–102 loss to the Houston Rockets.

[26] On July 6, 2023, Holmes, along with the draft rights to Olivier-Maxence Prosper, was traded from the Sacramento Kings to the Dallas Mavericks.

[27] On February 8, 2024, Holmes and a future first-round pick were traded to the Washington Wizards in exchange for Daniel Gafford.

[29] Listed at 6 feet 9 inches (2.06 m) and 235 pounds (107 kg),[30] Holmes has primarily played the center and power forward positions throughout his career.