She is the daughter of the late actor Vinod Mehra from his third and last wife Kira. She was less than two years old when her father died in October 1990. She was brought up in Kenya with her brother Rohan by her maternal grandparents. Soniya went to The Mombasa Academy in Mombasa, Kenya and completed her education in London. She began her training in acting at the age of eight in school where she earned the Gold Medal with an Honours at The London Academy of Music and Dramatic Arts Acting Examinations. She also took a short course at The Arts Educational Schools of London. When she was 17, she moved to Mumbai and joined Anupam Kher's 'Actor Prepares' for a 3-month course. Soniya is also a trained dancer, having started ballet when she was only 5 years old, she went on to do various forms of dance like street jazz, ballroom (which includes samba, tango, blues, and jive), Bollywood dance, kathak, hip hop and belly dancing.

She made her acting debut in Victoria No. 203, a remake of the 1972 classic and released on 31 August 2007. After the release of Victoria 203 which was a commercial flop, Soniya took a long gap of several years and made a comeback with a small role in Ek Main Aur Ek Tu in 2012. Soniya was seen in an interesting role in Ekta Kapoor's Ragini MMS 2, released on January 17, 2014. Soniya Mehra has also worked as a VJ on MTV India. She did various shows such as MTV Grind, MTV News, MTV Style Check etc.