In 2257, he graduated with James T. Kirk from Starfleet Academy and was a mutual friend of Kirk and Benjamin 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")