He was awarded a Rhodes scholarship to Oxford where he studied at Magdalen College, receiving a second Bachelor of Arts degree in 1974.
After graduating from Yale, he clerked for Judge J. Skelly Wright of the United States Court of Appeals for the District of Columbia Circuit.
He then clerked for Justice Harry Blackmun of the Supreme Court of the United States during the October 1977 term, before entering private practice in Houston.
On January 26, 1999, Ellison was nominated by President Bill Clinton to a seat on the United States District Court for the Southern District of Texas vacated by Judge Norman William Black.
[3] Ellison was confirmed by the United States Senate on June 30, 1999,[3] and received his commission on July 7, 1999.