Mount Thyestes is a mountain summit located in the Tantalus Range, in Tantalus Provincial Park, in southwestern British Columbia, Canada. It is situated immediately west of Brackendale, northwest of Squamish, and southeast of Mount Tantalus, which is the highest peak in the Tantalus Range. Its nearest higher peak is Omega Mountain, to the northwest, and Mount Pelops lies to the west-northwest. Precipitation runoff from the peak drains into tributaries of the Squamish River. The first ascent of the mountain was made in 1942 by R. McLellan, H. Parliament, and F. Roots. The mountain was named for Thyestes, son of Pelops, and grandson of Tantalus according to Greek mythology. The mountain's name was officially adopted on June 6, 1957, by the Geographical Names Board of Canada.