Tessy was associate project director of the 3,000 km range Agni-III missile project. She was the project director for mission Agni IV which was successfully tested in 2011. Tessy was appointed as the Project Director for 5,000 km range Agni-V in 2009 and is based at the Advanced Systems Laboratory in Hyderabad. The missile was successfully tested on 19 April 2012. In January 2012, Prime Minister Manmohan Singh told the Indian Science Congress that Mrs Thomas is an example of a "woman making her mark in a traditionally male bastion and decisively breaking the glass ceiling". The media loves to call her Agniputri, or one born of fire, after the missiles she has helped develop. "We are all proud of our country. Agni-V is one of our greatest achievements," she says.
She is married to Saroj Kumar, now a commodore in the Indian Navy and they have a son, Tejas. engineer in ford technologies.In a glowing tribute in 2008, The Indian Woman Scientists Association did not forget to mention that "like most women she also does a tight-rope walk between home and career, between being a mother and a scientist who is dedicated to her job. "We feel Tessy Thomas serves as a role model and an inspiration for women scientists to achieve their dreams and have their feet planted in both worlds successfully," the group said.