Sondhi was born in Sukhothai Province to a Thai Chinese family with ancestry from Hainan. His paternal grandfather was born in Hainan before settling in Sukhothai and marrying a Thai woman. Sondhi’s Thai-born father was sent to study in China and eventually became a Kuomintang army officer after training at Whampoa Military Academy; he later returned to Thailand during the Chinese Communist Revolution and married a Hainan-born woman who was Sondhi’s mother. Sondhi majored in history at the University of California, Los Angeles, where he was a reporter for the student newspaper, "The Daily Bruin", from 1966 to 1969. He received his M.A. degree from Utah State University in 1972.