Half Human and Half Betazoid, Deanna Troi is empathic rather than telepathic. She has served in Starfleet for twenty years, attaining the rank of Commander. Troi is one of the foremost experts on the psychology of long duration starship missions in Starfleet, and her expertise was recognised in 2364 with a posting to the Federation flagship. She served with distinction in the role of Counselor, but initially had little to to do with ships operations. In 2368 the Enterprise suffered a serious accident when it struck a quantum filament, and Troi was forced to take command of the damaged ship. Although she handled the situation successfully, the experience made her question her limited knowledge of operational matters. In 2370 Troi decided to expand her role on board the ship by taking the Commanders test in 2370. Although she found the technical areas difficult to master, she was eventually successful and was duly promoted to Commander. During the battle in which the Enterprise-D was lost, Troi replaced an injured crewman at the helm station; she subsequently undocked the ships saucer section when the warp core began to overload. The subsequent explosion knocked the main helm controls offline and threw the saucer section into Viridian III's atmosphere. Troi and Lieutenant Commander Data where able to control the re-entry and landing sufficiently to avoid any fatalities. Like most of the crew of the Enterprise, Troi was subsequently posted to the new Enterprise-E. During that ships mission into the past to ensure the success of Zephram Cochranes warp flight, Troi headed the ground control crew of the phoenix. She continued as ships Counselor on the Enterprise-E for six years before accepting a position on board the USS Titan, alongside her new husband Commander Will Riker, who was assigned to the captaincy of the ship. Shortly before the transfer Troi visited Romulus with the Enterprise-E, where she attracted the unwelcome telepathic attentions of the new Praetor, Shinzon. Troi was able to turn the tables on Shinzon during his battle with the Enterprise-E, using the telepathic link to locate his cloaked ship for the Enterprise to target. She also took the helm of the Enterprise for its ramming of the Scimitar.

Today Troi continues to serve aboard the Titan with her husband, Captain Riker.