Native of the planet Ocampa who left her homeworld in 2371 to join the crew of the Starship Voyager. Kes was born in 2370. Her father's name was Benaren. She had an uncle named Elrem. Kes's mother was a woman named Martis. Kes remembered her father as a wise man who did much to shape the person she became. Benaren died in 2371, when Kes was one year old. Kes, who was both inquisitive and intelligent, escaped her people's underground city in a quest to learn about her world. On the surface, she was captured and abused by the Kazon-Ogla until she escaped to the Starship Voyager, aided by Neelix, with whom she was in love. Kes demonstrated her gratitude and her love for Neelix shortly after stardate 48532, when she donated one of her lungs to save Neelix's life. Shortly thereafter, she began studying to become a medical assistant under the tutelage of Voyager's Emergency Medical Hologram. Her quarters on Voyager were located on Deck 8.

Kes believed there was truth to ancient legends that her people once had extraordinary mental powers. Shortly after joining the Voyager crew, she began to exhibit signs of such powers, including visions of a planet destroyed in another timeline by polaric ion energy and evidence of an eidetic memory. Kes studied Vulcan mind-control techniques under Tuvok's direction, on the theory that this would help her develop her natural Ocampan abilities. When under the influence of Tanis, she temporarily gained spectacular psychokinetic powers, giving her the ability to influence matter on a molecular level and to direct the flow of life-energy. In early 2372, Kes underwent early elogium, during whihch Neelix and she decided to conceive a child. She later learned that the elogium was a false one and that she might go though elogium again, later in life. Kes decided to wait until then to conceive a child. Kes continually strove to expand her knowledge and skills. She learned to pilot a Federation shuttlecraft under the tutelage of Lieutenant Tom Paris in 2372. Kes was surpried to learn that Paris found her attractive.

In 2373, Tieran of the Illari transferred his neural pattern into Kes's mind and used her body in his unsuccessful bid to take over the Illari government.

(In one possible future, Kes received bio-temporal chamber treatments in 2379, causing her cells to enter a state of bio-temporal flux, sending Kes out of temporal synch. Kes traveled backward in time, experiencing a series of brief visits to various points in her life. In one possible future, she and Tom Paris married and had a daughter, Linnis, in 2375. Linnis later married Harry Kim and the two had a son, Andrew, Kes's grandson. In this reality, Kes continued to work in sickbay and eventually became a doctor. Kes was eventually restored to temporal normality when she was exposed to a precisely modulated field of antichroniton particles.)

Between stardates 50953 and 51003, Kes was subjected to considerable strain due to interaction with Species 8472 and their phenomenal telepathic abilities. It is belived that telepathic contact with Kes provided Species 8472 with a great deal of information concerning Voyager and the Borg. It was though Kes that Captain Janeway was able to determine the true nature of Species 8472, leading to the cooperation between Voyager and the Borg to destroy Species 8472.

Following the retreat of Species 8472 through the dimesional rift. Kes's mental abilities accelerated quickly. Her telekinetic and mental focus became extraordinary while at the same time controlled. Kes's telekinetic abilities quickly became a danger to the Voyager, causing structural instabilities in the hull. It quickly became evident that Kes was experiencing an accelerated evolution into what is believed to be the Ocampan's next form of existence. With the help of Captain Janeway she was able to leave Voyager in a shuttlecraft prior to assuming her new form, which saved the Voyager from destruction. Following her depature, Kes gave the crew a gift by hurling Voyager some 9,500 light years forward, effectively seeing them out of known Borg space.