(written from a Production point of view)
She also played the mirror universe version of Jadzia in "Through the Looking Glass" and "Shattered Mirror", as well as Honey Bare in "Our Man Bashir" and Darlene Kursky in the acclaimed episode "Far Beyond the Stars".
Farrell was good friends with Marina Sirtis and Michael Dorn and several other cast members of Star Trek: The Next Generation before Deep Space Nine began. She was speaking to Sirtis when she got the call to go to Rick Berman's office, where she was told that she had gotten the role of Jadzia Dax.
In 1984, she starred in the short-lived television series Paper Dolls with her future DS9 guest stars Richard Beymer and Geoffrey Blake. (Blake is her second favorite DS9 guest star; her favorite guest star is John Glover, who starred in "Invasive Procedures".) The series also featured Jonathan Frakes, and several episodes were helmed by TOS directors Leo Penn and Ralph Senensky. In 1992, she played Cat in the second pilot of the American version of Red Dwarf. Despite playing the title role in the 1992 Quantum Leap episode "A Leap for Lisa" alongside Enterprise captain Scott Bakula and Enterprise guest star Dean Stockwell, she made only a brief appearance.
Among her film credits is 1986's Back to School (which also featured Sally Kellerman, Adrienne Barbeau, and Robert Picardo). In the same year, she also appeared in the made-for-TV movie The Deliberate Stranger, alongside Jeannetta Arnette, William Boyett and Lawrence Pressman.)
Farrell has very sensitive skin. At the beginning of season 5, the original script for "Apocalypse Rising" was to have Farrell as the fourth member of the infiltration team, as this made the most sense given her experience with Klingon culture. However, this had to be changed to having Colm Meaney play a somewhat clueless fifth wheel instead, due to Farrel's inability to tolerate the Klingon makeup. Ironically, Meaney hated the makeup so much that he was never asked to wear any again.
After six seasons on DS9, Farrell was presented with the chance to join the Paramount sitcom Becker. Instead of renewing her original contract for DS9 for one more season, she left and joined the cast of Becker in 1998 where she stayed for four years playing the character of Reggie Costas. There were many rumors as to why Farrell left DS9; some believed she wanted more money, there were differences with producers, or she had arguments with fellow cast members. In The Fifty-Year Mission: The Next 25 Years, Farrell revealed she had had enough of Berman, whom she described as a misogynist who regularly criticized her appearance. When her contract ended, she wanted to do less episodes, but he refused:
"Basically he was trying to bully me into saying yes [to another]. He was convinced that my cards were going to fold and I was going to sign up. He had [another] producer come up to me and say, 'If you weren't here, you know you’d be working at Kmart.' I was, like, 'What the hell are you talking about? I had a career before this. Why the hell would I be working at Kmart? Who are you?' Just to be jerky, he'd call me in my trailer: 'Have you been thinking about it yet? Are you going to sign?' Like, right before I had a scene. It was that kind of thing. Rick Berman said I was hardballing him, and I was, like, 'I'm not. I just want to have a conversation. You're giving me a take-it-or-leave-it offer and I’m not okay with that.' So I finally did have a conversation with him and asked to cut down my number of episodes or just let me out."
David Stipes, Visual Effects Supervisor for the episode in which Farrell made her last appearance, was present at the shoot and had this to say,
"Terry Farrell's contract was up on DS-9 and she was leaving the show. The story going around was that she did not wish to leave but the producers would not grant her contract requests. As the visual effects supervisor, I was on the DS-9 set to oversee the effects needed for her last scenes on the series. Terry was not very happy and was giving tearful goodbye hugs to her production crewmates. I have seen actors who were really obnoxious and uncooperative when they didn't get what they wanted so I was watching Terry with interest as the day unfolded. For every shot when called, she dried her tears, went on set, became her character, Dax, and delivered the best performances she could. She did not give an attitude, whine or make excuses. She did her job." Stipes was able to help Farrell out in the scene where her character was killed off. Continuing, he remembered:
"To give Terry an exit from the series, the DS-9 writers had bad boy Gul Dukat kill Jadzia Dax in the episode called 'Tears of the Prophets'. Dukat, possessed by the Pah-wraiths, uses an energy force to lift Dax off the ground then kill her. To accomplish this, Terry would have to wear a special flying harness which wrapped around her hips. Unfortunately the rig, made of thick leather and straps, was very uncomfortable and did nothing to flatter Terry's figure. In fact … she was horrified at how she looked. Terry came up to me with a look of desperation on her face; the harness around her hips made her look huge! Was there anything I could do to make her look better in her last shots?
I was so impressed with her qualities of character and professionalism that I assured her that I would do what I could to help her look good in the final shots. With that she appeared relieved and we went on to do the final death scene. When we got the footage into the digital compositing bay we began looking at techniques and options to see what we could do to help Terry regain her figure. Since we were on a budget for a limited effect for the death scene, we had to squeak this in somehow. We decided to cover Terry's torso and hips with effects elements rather then try to rotoscope or otherwise distort her filmed image frame by frame which would have cost a lot in man-hours and bay time.
Luckily, we had some resources. Over the years of production, we had amassed a collection of visual effects footage elements like fire, smoke and liquid nitrogen. We began experimenting with the elements over Terry's footage to see what worked. We decided to use licks of liquid nitrogen vapor fluttering out from the edge of the body and hiding her rig-thickened profile. While not a perfect fix, we did it within the budget we had. Months later at the DS-9 wrap party, Terry came over and gave me a warm thank you for making her look good. I told her how impressed I was with the way she handled herself in that situation so it was a pleasure to help her." 
After leaving Deep Space Nine, Farrell stated that, if asked, she would love to return to Star Trek to play Jadzia as a clone, Jadzia from another universe or a hologram. She also stated she grew greatly from playing Dax and that she wouldn't change a second of her time with Star Trek.
Farrell's character, Jadzia, was not seen as a part of the flashback sequences toward the end of "What You Leave Behind". This was because Farrell did not give the producers her permission to use pictures of her in those scenes. Although a scene was written for Jadzia in the final episode, budget costs meant they couldn't afford Farrell and the scene was never filmed.
At the Star Trek convention in 2007, Farrell said she wished she had not been so quick to leave Deep Space Nine, because "Jadzia Dax was the coolest character"; even Reggie can't compare: "It's hard to go from [playing] a hero to a neurotic, bad cook," she explained. At the Trek Las Vegas convention in the same year, she expressed her gratitude to the fans and their loyalty. 
At a Las Vegas convention in 2014, Farrell wore her Dax make-up and her costume from "You Are Cordially Invited". Before that, she wore a shirt reading "Dax-539" to commemorate the 539th time Michael Westmore would apply her Trill spots. 
After a long hiatus, in 2017 she appeared in the web-series Renegades, based on the fan film Star Trek: Renegades, playing the character Jada. This production features many Star Trek alumni, including Walter Koenig, Nichelle Nichols, Robert Beltran, Tim Russ, Gary Graham, Aron Eisenberg, Manu Intiraymi, Cirroc Lofton, and Hana Hatae. She also appeared in the anthology film The Circuit, again with many Trek alumni, including Intiraymi, Koenig, Doug Jones, Robert Picardo, Olivia d'Abo, Armin Shimerman, Robert Beltran, Tim Russ (who also wrote and directed), Ethan Phillips, J.G. Hertzler, and Hana Hatae.
Additional Star Trek characters
|Star Trek: Deep Space Nine regular cast|
|Rene Auberjonois • Avery Brooks • Nicole de Boer • Michael Dorn • Terry Farrell • Cirroc Lofton • Colm Meaney • Armin Shimerman • Alexander Siddig • Nana Visitor|
Star Trek interviews
- What We Left Behind
- TNG Season 7 DVD special feature "Star Trek: Deep Space Nine DVD Preview"
- DS9 Season 1 DVD special feature "Section 31-Hidden File 05", interviewed on 30 September 1992
- DS9 Season 1 DVD special feature "Section 31-Hidden File 06", interviewed on 30 September 1992
- DS9 Season 1 DVD special feature "Deep Space Nine Scrapbook Year One", interviewed on 30 September 1992
- DS9 Season 2 DVD special feature "Crew Dossier: Jadzia Dax", interviewed on 14 October 2002
- DS9 Season 2 DVD special feature "Section 31-Hidden File 05", interviewed on 14 October 2002
- DS9 Season 2 DVD special feature "Section 31-Hidden File 07", interviewed on 14 October 2002
- DS9 Season 6 DVD special feature "Section 31-Hidden File 01", interviewed on 14 October 2002