Early in his career, Thomas Eugene Paris served aboard the Starship Exeter. He majored in astrophysics at Starfleet Academy. As an academy cadet, Paris chose the Starfleet base outside Marseilles, France for physical training in his second semester of the academy. He spent most of his time that semester at Chez Sandrine, a bistro that he later re-created in the holodeck of Starship Voyager.

The son of a Starfleet admiral, Tom Paris was a graduate of Starfleet Academy and was involved in a fatal accident that claimed the lives of three other Starfleet officers. Paris initally denied responsibility for the accident, but later admitted he had falsified reports to hide his culpability, and was forced to leave Starfleet. In later years, Paris realized that his greatest mistake was not having told the truth. Paris became a mercenary for the Maquis, but was arrested by Federation authorities while on his first assignment for the resistance group. He was imprisoned at the Federation Penal Settlement in New Zealand on Earth, but was released in 2371 at the request of Voyager Captain Kathryn Janeway. In exchange for his parole, Paris agreed to help the Voyager locate his former colleagues in the Maquis. While carrying out this mission, Paris and all Voyager personnel were swept into the Delta Quadrant, where they were forced to join forces with the Maquis crew in order to survive. Janeway subsequently reinstated Paris's Starfleet commission and assigned him to the ship's conn. Paris experienced some discomfort at working under Commander Chakotay, a former Maquis officer.

In 2372 Paris made history by becoming the first human pilot to cross the transwarp threshold and attain a warp 10 velocity. The experience accelerated the evolutionary process in his cellular DNA, mutating him into an amphibious creature. Fortunately, Voyager's Emergency Medical Hologram was able to reverse the process. Voyager Captain Kathryn Janeway was also mutated by Paris's transwarp flight, and while mutated, the two had three amphibian children, which they left on a planet in the Delta Quadrant.

Tom Paris was an aficionado of 20-th century America, and was fond of traditional Earth foods from that period. He was an experienced rock climber and was skilled at spelunking.

Tom Paris realized in 2372 that he was very much attracted to Kes. He decided not to act on these feelings out of respect for Neelix, who was, at the time, involved with her. Paris was an instrumental part of an elaborate scheme devised by Janeway and Security Chief Tuvok, intended to trap a spy believed to be operating aboard Voyager. Paris exhibited increasing anger and discontent with his life aboard the ship for several weeks in 2372, culminating with his departure from the Voyager crew. In doing so, Paris was able to determine that Michael Jonas had been acting as a Kazon operative, working against the interests of the Voyager crew.

(In one possible future, B'Elanna Torres and Tom Paris became romantically involved. Later, Torres and Captain Kathryn Janeway were killed in a Krenim attack. Paris was devastated. Kes comforted him, helping him get through the pain, and the two ended up together. Kes and Tom Paris married and had a daughter, Linnis, in 2375. Linnis later married Harry Kim, and the two had a son, Andrew Kim, who was Tom's grandson.)