Sonam was born in Darjeeling to Tibetan refugee parents. His father, Lhamo Tsering, who was born in the Kumbum area of Amdo (Chinese: Qinghai Province), served as Chief of Operations for the Tibetan resistance movement from the late 50s until the early 70s, and later, as a Minister in the Dalai Lama’s government-in-exile. His mother, Tashi Dolma, was from a village near Lhasa in central Tibet.
Sonam studied at the Jesuit boarding school, St Joseph’s College, in Darjeeling. He did his undergraduate studies at St Stephens College, Delhi University. After a year each at Scottsdale Community College in Arizona and Santa Monica College in California, he went to the University of California, Berkeley’s Graduate School of Journalism where he specialised in documentary filmmaking.
After his graduation from Delhi University in 1978, Sonam worked for a year in the Security Department of the Tibetan government-in-exile in Dharamshala. He then worked as a dishwasher in Manhattan, a gardener in Scottsdale and a janitor in Berkeley. He was the manager of Del Rey Car Wash in Marina del Rey, California, for a year. After graduating from Berkeley, he worked for four years as Programming Director at the Meridian Trust in London, along with his partner Ritu Sarin. In 1991, he and Sarin founded White Crane Films. He has been an independent filmmaker ever since.
In addition to his role as a filmmaker, Sonam is an essayist and a writer. In 1979, along with the late writer, K. Dhondup, the scholar Tashi Tsering, Thupten Samphel, Kesang Tenzin and Gyalpo Tsering, he founded the pioneering English-language Tibetan poetry journal, Lotus Fields. He wrote the script for the feature film, Dreaming Lhasa. His writings have been published in Civil Lines, The Hindu, Time magazine, and Himal Southasian. His travel piece, A Stranger in My Native Land, was published in Written Forever: The Best Of Civil Lines. 
Sonam and Sarin are married and have two children. In 1996, they moved to Dharamshala, the exile home of the 14th Dalai Lama and the epicentre of the Tibetan diaspora, to raise their children. They have been based there ever since.
Sonam's first film was the student film, Mark Pauline: Mysteries of a Mechanical Mind (1984), which he co-directed with fellow Berkeley classmates, Steve Evans and John Sergeant. A portrait of maverick Bay Area artist Mark Pauline, the film won Third Place at the 1984 Student Emmys. Since then, all his film have been made in partnership with Ritu Sarin. These include:
|1985||The New Puritans: The Sikhs of Yuba City|
|1991||The Reincarnation of Khensur Rinpoche|
|1993||The Trials of Telo Rinpoche|
|1997||A Stranger in My Native Land|
|1998||The Shadow Circus: The CIA in Tibet|
|1999||Big Treasure Chest for Future Children: Tibet|
|2000||rights... & wrongs|
|2007||The Thread of Karma|
|2007||Some Questions on the Nature of Your Existence|
|2009||The Sun Behind the Clouds: Tibet's Struggle For Freedom|
|2012||When Hari Got Married|
- Krishna, Nakul (February 2010). "Those Bloody Indians in a Major Key". The Caravan. Retrieved 26 October 2013.
- Bennett, Bruce (April 13, 2007). "Wandering Tibet For a Piece of Home". New York Sun. Retrieved 3 September 2012.
- "Some Questions on the Nature of Your Existence". T-BA21. Retrieved 3 September 2012.
- Thomas, Kevin (June 24, 2010). "Movie Review: 'The Sun Behind the Clouds: Tibet's Struggle for Freedom'". Los Angeles Times. Retrieved 3 September 2012.