In 2257, he graduated with James T. Kirk from Starfleet Academy and was a mutual friend of Kirk and Ben Finney. Timothy and Kirk served together during the Vulcanian expedition, they would not see each other again for some time after that.
In 2267, he was an operations division officer. In Starbase 11's M-11 Starbase Club, Timothy confronted Kirk following the apparent death of Finney, blaming Kirk for killing his friend. (TOS: "Court Martial")