Deanna was born on Betazed in 2336. Her human father, Ian Andrew, was a Starfleet officer who died when Deanna was only seven years old. Her Betazoid mother, Lwaxana Troi, a remarkable person, is ambassador to the government of Betazed, daughter of the Fifth House, Holder of the Sacred Chalice of Rixx and Heir to the Holy Rings of Betazed.
Before joining Starfleet, Deanna studied psychology at the University of Betazed. While a psychology student, Deanna became romantically involved with Lieutenant William T. Riker. She had hopes of a serious commitment between the two, but Riker's career plans took him away to an assignment aboard the U.S.S. Potemkin. She graduated from Starfleet Academy in 2359.
In 2365, Deanna was involuntary impregnated by an unknown noncorporeal life-form. She named the child Ian Andrew Troi, after her late father [episode: 'The Child']. However, Andrew died a few days after being born.after experiencing human life and then death.
Deanna suffered a brief loss of her empathic powers in 2367 from proximity to a newly discovered group of two-dimensional creatures [episode: 'The Loss']. Although she found the loss disconcerting, she was pleased to discover that she could still function as ship's counselor without her Betazoid abilities.
Deanna assumed temporary command of the Enterprise-D on stardate 45156 when the ship was damaged from collision with two quantum filaments [episode: 'Disaster']. Deanna, who held the rank of Lieutenant Commander, was the senior officer on the bridge at the time.
Marina Sirtis originally auditioned for the part of Natasha Yar and was almost cast for the part, but Gene Roddenberry decided at the last moment to switch the roles of Yar and Troi between Sirtis and Denise Crosby.