Kes is an Ocampa, an intelligent, telepathic species who has a nine-year life span. The Ocompa live in an underground city on the Ocampan homeworld, which is a world covered by one huge desert. Centuries before, the Ocampa city was built by The Caretaker, who vowed to take care of the Ocampans and supply them with energy and water. In 2371, the Caretaker became ill. Knowing he was dying, he increased the energy supply and began a search across the galaxy to find a male and female who could take his place. This search brought the Federation starship U.S.S. Voyager and the Maquis vessel Liberty to the Delta Quadrant.

In 2371, her father Benaren and then her mother Martis died when she was one year old. Being very curious, she heard about the surface and decided to explore. When she got to the surface, she was captured by the Kazon-Ogla, who wanted to steal the Ocampa's unlimited energy and water supply. Kes was then rescued by Neelix and the U.S.S. Voyager crew from the Kazon-Ogla and she left the Ocampa Homeworld and joined Voyager's crew. She soon became the EMH Doctor's medical assistant.

In 2374, Kes' body went into a state of cellular flux and she experienced uncontrollable psychokinetic abilities which endanged the ship. When Ocampa's die, they move on to a new "plane of existence." While no definite reason why Kes resonated early is given, the EMH Doctor theorized that her interaction with Species 8472 had caused it.