Prior to his Bollywood career, Samir was an investment banker with one of the bulge bracket firms on Wall Street in New York, before coming back to India to start modeling. He has attended acting courses in New York and Los Angeles.
Soni made his debut in the Hindi serial Samandar based on Navy officers. In 1996, he appeared as Ashok Mathur in Doordarshan's A Mouthful Of Sky, based on Ashok Banker's script and directed by Mahesh Bhatt. He made his film debut opposite actress Mamta Kulkarni in China Gate (1998), though it was followed by forgettable cameos in films.
In 2003, Samir shot to fame by appearing in the film Baghban and played lead roles in Basti and Kahan Ho Tum. In that same year, Soni also worked in the popular television series Jassi Jaissi Koi Nahin that aired on Sony. In 2004, he worked in another popular show on Sony channel called Saaksshi.
Soni featured as one of the contestants in the reality television show Bigg Boss 4 in 2010. He was evicted from the house a week prior to the grand finale.
Through modeling, he met his ex-spouse, Rajlakshmi Khanvilkar. The two were married for six months before they divorced. He also dated late model, Nafisa Joseph.
On 24 January 2011, he married former actress Neelam Kothari.