Tom Paris is a graduate of Starfleet Academy. His father is Admiral Owen Paris. During his last year at starfleet academy, Tom was involved in an shuttle accident which killed his three best friends (Charlie Day, Odile Launay and Bruno Katajavuori). He lied about the incident, but later confessed, and was discharged from starfleet.
He came to Voyager after serving in Federation Penal Settlement near Auckland, New Zealand after piloting for the Maquis. In 2371 the USS Voyager, along with a Maquis ship, was brought across the galaxy by a creature known as 'The Caretaker' and were stranded there. The Maquis ship was destroyed and the its crew joined Voyager's crew. (The Caretaker)
In 2372 he, with Captain Janeway attempted to break the Warp 10 threshold and achieve infinite speed. This then caused both him and Janeway to 'evolve' at a greatly accelerated pace. Eventually, The Doctor was able to revert them back to their normal state. (Threshold)
In early 2374 he was assigned additional duties to sickbay to assist The Doctor, the original medical staff having all been killed earlier. (Revulsion)
In 2375 he was demoted to ensign and put in solitary confinement for thirty days after violating the Prime Directive. (Thirty Days) He was reinstated to his former rank in late 2376.
Tom Paris and B'Elanna Torres entered into a relationship in 2374 and on February 2, 2377 they got married. (Day of Honor and Drive) Note that they appear to get married in Course: Oblivion, but this isn't in fact them.
In December of 2377, their daughter was born just as Voyager reached Federation territory. (Endgame, Part 2)
Tom's character is based on Nick Locarno from The First Duty (TNG). They were going to be the same person but the producers decided Locarno was incorrigible so they decided to make them different people.
According to a large number of fans, the reference to "The Ghosts of Those Three Officers, came back and taught me the true meaning of Christmas" was originally ment to be sarcastic remark to Harry Kim. However, some took it to be literal. The Similarities between Paris and Locarno also show that they are infact the same person, Paris having used an Alias, and his mother's last name as to not receive any special "favors" in Starfleet Academy because of his father's positions. After being kicked out of Starfleet, he reverts back to his real name, and then travels out on his own. He joined the Maquis and was arrested on his first mission. Setting the stage for the beginning of Voyager.
Tom Paris is played by Robert Duncan McNeill.