As a freshman at Florida SouthWestern, Ellis averaged 8.3 points and three rebounds per game, earning Second Team All-Suncoast Conference honors.[3][5] On January 4, 2020, he scored a school-record 41 points in a 92–77 win against St. Petersburg College.[6] In his sophomore season, Ellis averaged 18.1 points, 4.3 rebounds, 2.2 assists and 2.1 steals per game, setting program single-season records in points and steals. He was recognized as a Second-Team NJCAA Division I All-American and Suncoast Player of the Year.[7][8] For his junior season, Ellis moved to Alabama, choosing the Crimson Tide over Iowa State, Kansas State and Western Kentucky.[9]
He averaged 5.5 points and four rebounds per game as a junior.[10] Ellis was named to the SEC All-Defensive Team as a senior.[11] He averaged 12.1 points, 6.1 rebounds and two steals per game.[12]
Ellis played in seven total games during the 2022 NBA Summer League, averaging 11.4 points on 44.1% shooting from the field and an impressive 46.9% from three, 3.6 rebounds, 3.3 assists and 2.0 steals per game.
On July 2, 2023, Ellis signed another two-way contract with Sacramento[15] and on February 9, 2024, he signed a multi-year contract with the Kings.[16] On April 9, Ellis scored a career–high 26 points in a loss against the Oklahoma City Thunder. On April 17, Ellis helped the Kings to a play-in tournament victory over the Golden State Warriors, with 15 points, five assists, four rebounds, three steals and three blocks.[17]
On November 18, 2024, Ellis scored a new career-high 33 points with 9 three-pointers in a loss against the Atlanta Hawks.[18]