During the 2360s, Masters was assigned to guard a deuridium storage facility on Kobliad during the unrest caused by a attack on the planet. The facility was breached by criminals and Masters was shot and nearly killed. (Star Trek: The Farthest Star: "Ripples")
In 2366, Masters had reached the rank of lieutenant and was serving on the USS Parthian. During that year the ship was involved in the Hyralan Incident in which Masters was heavily involved rescuing hundreds of lives. He was later rescued by the USS Swiftfire, but sustained serious injuries. In the aftermath there was some controversy around his actions due to a number of deaths during the incident. (Swiftfire: "First Choice")
After recovering from his injuries Masters was assigned to the USS Bougainville as its security chief. During his time on the Bougainville he was promoted to lieutenant commander. (Swiftfire: "First Choice")
In 2369, Masters was assigned to the USS Swiftfire at the request of Captain Eloise Allston to replace her outgoing first officer. As part of this assignment he was promoted to commander. (Swiftfire: "First Choice")
The being known as Harbinger referred to Masters as "the Destroyer" due to Masters apparent pivotal role in a galaxy wide catastrophe. The Harbinger attempted to avoid this by killing Masters in the past. He travelled back to the events on Koblaid and changed events that resulted in Masters being shot and nearly killed.
In a subsequent vision Masters was shown in command of the USS Swiftfire-A visiting the world the Harbinger resided on. He was also possibly tied to a catastrophe on that world. (Star Trek: The Farthest Star: "Ripples")
Masters had a very close relationship with Susan Core that was formed over the two years they served on the USS Bougainville. When considering whether he wanted to transfer to the USS Swiftfire his relationship with her was an important factor he took into account. (Swiftfire: "First Choice")