The youngest child of Fran Preston, sister of Montgomery Scott, Peter was born in Scotland in the 2260s. Peter was also the younger brother of Dannan Stuart (born 2264). (TOS comic: "Retrospect"; TOS novel: Enterprise: The First Adventure) (Fran's name is given as "Clara" in TNG novel: A Time for War, A Time for Peace.)
Peter took his uncle's advice and was a midshipman first class serving aboard the USS Enterprise by 2285. During what was supposed to be a simple training cruise on board the Enterprise, Preston was training with the ship's engineering crew when the vessel was attacked by the notorious Khan Noonien Singh. During the attack, Preston remained at his post, stopping a dangerous leak. He also saved the life of injured classmate Nancy Bryce by pulling her out of harms way. (TOS comic: "Who's Who in Star Trek 1")
- In the novelization of Star Trek II: The Wrath of Khan, Peter's age was given as 14 and stated that he had a sister who was 12 years older than him. This information seems to be false as it seems unlikely a 14-year-old would have enrolled in Starfleet Academy. Another piece of evidence is that his sister was born in 2264 (as stated in Enterprise: The First Adventure, by the same author), which means he would have been born in 2276. Another point against is that both children appeared in "Retrospect" in the early 2270s, and they appeared of similar ages.
Peter's memorial service on Earth was a closed casket ceremony conducted by a Starfleet chaplain. After the service, Peter's mother Fran Preston slapped her brother Montgomery's face for commanding the section where Peter was killed. Montgomery's wife Glynnis Campbell tried to calm the grieving mother, but Montgomery was again confronted, this time by Peter's sister Dannan Stuart. Dannan was headed back to a posting at Starfleet Academy, where she informed her uncle she would be carefully reviewing log entry recordings associated with her brother's death, looking for ways Montgomery might have saved him. Saavik assured Scotty that it was obvious he was not at fault for anything that took place during the incident. In the time following the ceremony, Scott confessed to his wife that at the time he gathered up his nephew's dying body, he would have gladly given up his reputation as a miracle worker to be able to actually perform a miracle and bring Peter back.
In a drunken conversation with James T. Kirk and Leonard McCoy in 2286, Scotty referred to Peter's death as an "accident", indicating that he might not have placed very much blame against anyone in particular for the occurrence, despite the fact that the phaser fire that caused the engineering deaths had been maliciously ordered by Khan Noonien Singh, and had been badly received because Kirk had failed to follow Starfleet regulations and raise full deflector shields against Khan's Reliant. (TOS comic: "Retrospect")