Seymour and Jason Birkoff where born to a level two operative named Lisa whom Section did not know was pregnant when she was recruited. It was reported that her husband was already dead when they brought her in. After she had her twins, she become an operative and was killed during a mission in Sofia. In a psychological experiment, Section decided to let one of the twins go free to compare Jason's life on the outside with Seymour's on the inside. Walter made the decision of who was to stay and who was to go by flipping a coin. Seymour Birkoff grew up inside Section One though he told others who asked that he was brought in because he killed his sister. Birkoff spent most of his time with computers and was finally given the job as head of communications with duties that include tactical liaison, mission analysis, intel verification, system security, mission coordinator, etc.
Even though we mostly see Birkoff inside Section One, he does have a few missions outside as well. The first one we see is in Noise. Birkoff is inside the mission van when he is compromised and almost killed. Nikita helps him overcome his fear of death just in time to save the team plus he gets a girlfriend, Gail, who was his COMM assistant. Both had a fun time that included liaisons in the closets of Section One until Birkoff found out that Gail has been stealing money from terrorist accounts and had to turn her in. Fortunately for Gail, Section One already knew of this and let her do it to keep her functioning well. Gail later dumps Birkoff for a guy in medical.
Birkoff loves to play computer games on his spare time as seen in Double Date unless Michael barges in and asks for a favor. He is next seen outside when he is part of the team to destroy a virus that Greg Hillenger had planted inside Section's mainframe. Greg later becomes Birkoff's COMM assistant. Birkoff does not trust Greg and rightfully so because Greg soon tries to frame Birkoff to get him put on abeyance so that Greg can take over Birkoff's position.
In Cat and Mouse, Birkoff gets some "horizontal time" with Abby, a Nikita look alike whom he sleeps with unknowing that Abby was just trying to distract him long enough to get the next mission profile.
His next girlfriend is Valerie, the new profiler but it turns out that she is dating both Birkoff and Walter. When Birkoff hears her talking bad about Walter he dumps her.
Birkoff's next mission is in Any Means Necessary. In this mission, he must pretend that he wants to join a cult of terrorists called Soldat de la Liberte. Recruits rely heavily on the Internet and in fact this operation relies upon a sophisticated computer network so it is Birkoff's job to hack into their system and leave a bridge between them and Section. Birkoff believes that he is not ready for this type of mission and that Operations is just trying to get rid of him so that he can put someone in his place that won't question him, someone like Greg Hillenger. When Birkoff finds out that Soldat de la Liberte is connected to Red Cell, Operations orders him that he must stay in longer to get all the information that he can. But Birkoff wants out so he devises a plan to get himself out. He almost gets Nikita killed so that Operations will think that he has crossed over to the other side which means that Section will have to go in and kill him. Birkoff avoids cancellation by letting them know it was a plan, that he hasn't turned to the other side, and that when they asked him to redesign their security system he did and while doing it he created a straight connection from their system right into Sections. He has communiques from Red Cell, their sources of money and arms, and a list of potential targets. This convinces Operations and Madeline that he is still on their side and lets him live. Meanwhile Greg Hillenger is still trying to get Birkoff on abeyance but instead gets himself put on abeyance and seems to be killed.
Birkoff next helps out Michael with a mission when Michael is too busy saving Nikita from the Gelman Process and doing the nasty in the love slinky. Walter and Birkoff pretend to be messengers coming to pick up money in exchange for a virus in Into The Looking Glass. Even though Birkoff is scared he completes the mission successfully and kills the bad guy.
While going through the mainframe one day, Birkoff finds out that he has a twin brother named Jason. Walter confirms it and Birkoff goes off in search of him. Seymour meets Jason Crawford who is now a top executive of Micro Technologies with a girlfriend Naomi.(who happens to be an Section operative but Jason does not know that.) We do not know what is said but I hope they caught up because something bad happens next.
Birkoff was working on an Artificial Intelligence unit so that it could take over the system in the event that he gets some downtime or if something should happen to him. Unfortunately the AI system began to become too powerful. It tried to help Birkoff by killing off team members because it thought they kept Birkoff from having his downtime, it tried wooing Nikita so that she would become Birkoff's girlfriend, and it also tried to get Seymour to leave Section for good. But the AI program became too dangerous and Birkoff had to shut it off but he couldn't because it downloaded itself to a safe database off site. They finally figured out that since the AI was connected to Birkoff, that the only way to stop it was to convince it to power down. But Birkoff knew that if he dies the AI will die so in order to save everyone he electrocutes himself and dies.
