Assimilated at an early age, Seven of Nine remained a part of the Borg Collective for eighteen years, serving most recently as Tertiary Adjunct to Uni-matrix 01 within the Collective. Seven of Nine served as the liaison between the Borg Collective and the Federation Starship Voyager during the war with the malevolent Species 8472. Her specific function was to assist Federation Captain Kathryn Janeway and Lieutenant Tuvok in developing a biogenic weapon that would defeat Species 8472, which had been attacking the Borg Collective in their realm within the Delta Quadrant. Seven of Nine had several confrontations with crewmembers of the starship Voyager, most notably when Commander Chakotay (in temporary command as Captain Janeway recovered in sickbay), depressurized the deck which the Borg were located on, sending all but Seven of Nine into space. Despite these difficulties, the alliance between the Borg Collective and Voyager proved successful, and with the success of the biogenic weapon, Species 8472 withdrew from Borg space and returned to their own realm. Seven of Nine attempted to gain control and assimilate the Starship Voyager once Species 8472 had been defeated, but her link to the Collective mind was severed when Commander Chakotay utilized Borg technology to appeal to her human side. Seven of Nine was taken to sickbay, where her human genes began to re-emerge. Captain Janeway decided to keep Seven of Nine aboard Voyager, since she was responsible for severing her link to the Collective. Captain Janeway's hope is that Seven of Nine will choose to remain with aboard the ship, since they can offer her the one thing that the Borg Collective could not... friendship.

Now severed from the Collective, and with her human genes resurfacing, Seven of Nine's body began to have violent, life threatening reactions to this process. Her Borg implants began to fight back, attempting to preserve her assimilation, and Captain Janeway ordered the Holographic Doctor to remove her Borg implants entirely. The Doctor, having studied Borg implants extensively from previous encounters, was successful in removing 87% her implants. Once this process had been completed, Seven of Nine's human genes were able to regenerate and she was restored to near total humanity. She has reluctantly decided to remain onboard the starship Voyager, realizing that being amongst a group of humans is the most suitable place for her to re-discover her own sense of individuality and humanity.

Captain Janeway was able to provide Seven of Nine with some information concerning her life prior to her assimilation. Her human name was Annika Hansen, born on stardate 25479 at the Tendara Colony. Her parents were both scientists who had originally set out to explore the Delta Quadrant aboard the research vessel U.S.S. Raven.

Shortly after stardate 51186, Seven of Nine recieved what she believed to be the homing signal from a Borg Cube, followed with episodes of hallucinatory visions of Borg drones and a black bird. Following these episodes, the remaining Borg implants began to regenerate. Seven of Nine subsequently escaped Voyager after commandeering a shuttle, in search of the source of the homing signal. Lieutenant Paris and Lieutenant Commander Tuvok pursuing in anouther shuttlecraft quickly found Seven of Nine's shuttle and attempted to board it. Seven of Nine anticipating the boarding quickly setup a containment field, trapping Tuvok in the aft compartment. Seven of Nine then disabled the other shuttle, leaving it adrift. The homing signal was traced to a planet where Seven of Nine found the remains of the U.S.S. Raven (NAR-32450). Seven of Nine proceeded to relive her experiences on the ship prior to her assimilation. Voyager later found Lieutenant Paris's disabled shuttle and traced the flight path of Seven of Nine to the planet. Following a short skirmish with the B'Omar who were attempting to destroy the Raven, Voyager succeeded in retrieving Seven of Nine and Tuvok.

Most of the information provided by the Borg Queen.