Sub-Commander T'Rul was a Romulan officer temporarily assigned to the USS Defiant, in 2371, to operate and guard a cloaking device her government had loaned to the Federation for covert exploration of the Gamma Quadrant.
Several hours after the Defiant entered the Gamma Quadrant, the starship (or at least its subspace variance) was detected by two Jem'Hadar attack ships. T'Rul was aware of this phenomenon that had been a closely guarded Romulan secret. On her advice, the ship dropped out of warp. After the Dominion ships began sweeping the area with an anti-proton scan, T'Rul admitted that she was unsure if it could penetrate the cloak.
After the Defiant was boarded by the Jem'Hadar, T'Rul was able to kill one of the invaders using her disruptor. After doing so, she was injured by another Jem'Hadar soldier.
Along with other members of the Defiant, T'Rul was taken to the Founders' homeworld and placed in Borath's elaborate simulation of Dominion treaty negotiations with the Starfleet officers. During the simulation, she was incensed that the Romulan government had been excluded from the peace talks and threatened war.
T'Rul and the others were freed from the simulation when Odo and Kira Nerys discovered them. She later returned to the Alpha Quadrant with the others. (DS9: "The Search, Part I", "The Search, Part II")