Magness was born in Texas and grew up in Bozeman, Montana. His father was Bob Magness, the founder of Tele-Communications Inc.. He attended the Western State College of Colorado, but dropped out.
Through his inheritance, he is a large stockholder in Tele-Communications Inc. He also chairs the Magness Investment Group, whose portfolio includes Magness Land & Cattle, Fortrust, a Denver-based state-of-the-art data center, and aquaculture breeding farms. In 2007, he founded Smokewood Entertainment with his wife, Sarah Siegel-Magness. He has produced three films and he is producing a fourth one. He has made charitable donations to the Food Bank of the Rockies, the University of Denver, and The Fresh Air Fund. He collects vintage cars.