The Supreme Council was a ruling body on Gallifrey. (TV: The Invasion of Time, PROSE: Cold Fusion, et al.) While one account indicated this Council was a briefly-renamed version of the High Council, (PROSE: A Brief History of Time Lords) another indicated that they were separate bodies which operated simultaneously. (PROSE: The Infinity Doctors) Accounts of Gallifrey before the First Doctor's era indicated the Supreme Council was the dominant governing body. (PROSE: Cold Fusion, The Gallifrey Chronicles)
A Supreme Council also existed on the Time Lord society on the Needle. (PROSE: Father Time)