Peter James Kirk (TOS novel: Sarek), was born in April 2252 (TOS novel: Avenger) as the eldest son of George Samuel Kirk, Jr. and Aurelan Kirk, and resided on the planet Deneva with his family. He had two brothers, Alexander and Julius Kirk.

In 2266, neural parasites struck Deneva, and killed his father. Peter and his mother were rescued by his uncle, James T. Kirk and the USS Enterprise (NCC-1701), although his mother died in sickbay. (TOS episode: "Operation -- Annihilate!") Unlike his brothers, who were on Rigel IV when the neural parasites struck, Peter was taken to Starbase 10 by the Enterprise, and later returned to Earth to live with his grandmother, Winona who raised him. (TOS novel: The Last Roundup) The Starfleet captain spent all his shore leave with his brother's children after their parents' death. Jim Kirk thought the children would be best raised by Aurelan's sister and her brother after he considered leaving Starfleet and adopting the kids himself. (ST comic: "Bloodline")

In 2267, Peter temporarily resided on Nador, and was captured by Nadorian terrorists protesting the planet's admittance to the Federation. (TOS novel: Gemini)

Peter eventually became the chief research scientist aboard the USS Feynman. The ship encountered an emergency and crash-landed while investigating the phenomenon known as a "black smoker." Peter was angry at James Kirk because of Kirk's well-known adventures overshadowing his own father's work. The captain saved Peter's life, along with the lives of the other Feynman crew and his own landing party. A month later, they had made amends when both visited the grave of Aurelan and George. (ST comic: "Bloodline")

In 2293, Peter was drugged and kidnapped by members of the Keep Earth Human League and (unbeknownst to the KEHL) handed over to the Klingon Kamarag who wanted to use him as a way to lure and kill his uncle. Kamarag held Captain James T. Kirk responsible for the death of his protegee, Kruge, who died on the Genesis Planet. (ST movie: The Search for Spock) However, this plan backfired on him spectacularly when Peter and his Kamarag's niece Valdyr fell in love and escaped from his compound. (TOS novel: Sarek)