Much of Chell's past remains a mystery. During the final events of Portal, GLaDOS mentions numerous times that Chell was abandoned at birth, and also mentions that she was adopted, and such references continue throughout Portal 2, although the credibility of GLaDOS' word is unclear. Many of GLaDOS' comments throughout Portal 2 and the latter stages of Portal are in an effort to belittle, annoy or distract Chell from achieving her goal, and whether or not statements of her adoption and orphan status are true or not is up for debate.
During the events of Portal 2, it is implied that Chell may be the daughter of a scientist who worked at Aperture Science.
Some time after GLaDOS' takeover of Aperture Science, Chell is awakened in a Relaxation Vault after being unconsciously placed into it. Curious, she explores the Vault, and within only ten seconds of awakening, Chell is greeted by a robotic and seemingly automated female voice who informs her that she is a test subject. A voice, (later to be revealed as GLaDOS) then states that Chell will be undergoing testing for the benefit of Aperture Science's research program.
GLaDOS then generates two oval-shaped teleportation fabrics (portals) on a solid flat surface, with an entrance portal in the Relaxation Vault and an exit just in front of the exterior of the Vault. Chell exits from the Vault, however she notices empty observation rooms which lack the staff that should be recording her performance. After completing her first test and acquiring an understanding the cube-and-button based mechanic, she is put through a series of tests to further explore and understand the use of portals.
Having completed two tests, Chell reaches a test chamber in which she acquires the Portal Gun. Later on during the testing course, she is put through a series of more dangerous tests including hazards such as Goo and High Energy Pellets, among others. Skillfully avoiding these hazards, Chell is assisted by the Companion Cube and by the Aperture Science Advanced Knee Replacement components applied to the back of her lower legs to her ankles, which allow Chell to avoid injury when falling from great heights. Eventually, the single-portal variant of her Portal Gun is upgraded to create a set of linked portals. As an incentive to complete the tests, GLaDOS promises Chell that cake will be served once all tests chambers have been completed.
As the testing progresses, Chell stumbles across various areas with defunct wall panels, and manages to sneak into them. As she enters these maintenance areas, she finds refuge areas commonly known as the Rat Man's Dens, previously used as hiding places by Aperture technician Doug Rattmann. The scribblings on the walls in these Dens appear to be warnings for Chell, telling her that "the cake is a lie" and that "she's watching you". Chell, now made more aware of her situation, is forced to continue testing and play along with GLaDOS' plans. The Rat Man's warnings are eventually revealed to be correct, as GLaDOS attempts to murder Chell upon her completion of the final test chamber, despite earlier promises of cake.
Chell successfully escapes the dramatically slow death trap, and is informed by GLaDOS that pretending to kill Chell is simply part of the test. Dubious as to the veracity of this claim, Chell escapes the testing course, and travels through the Aperture Science Facility in an attempt to reach the surface and escape. Eventually however, Chell realizes there there is no chance of escape as long as GLaDOS is in control of the Facility, and is forced to confront GLaDOS in the Central AI Chamber.
Upon entry to the chamber, Chell is greeted by the passive-aggressive rogue AI. GLaDOS claims that she will provide Chell with a surprise, however a Morality Core unexpectedly detaches from GLaDOS' chassis. Chell destroys it using a nearby Emergency Intelligence Incinerator, however the Core is revealed to be a safeguard designed to inhibit GLaDOS' homicidal tendencies. With the Core destroyed, GLaDOS releases neurotoxin into the chamber in an attempt to kill Chell. At the same time, a Rocket Turret emerges from a core hatch beside GLaDOS and begins to target Chell. Using the Portal Gun, Chell redirects the projectiles through linked portals, causing the rockets to strike GLaDOS, each of which detaches more Personality Cores from the chassis. Although inflicting damage, the loss of the Cores merely increases GLaDOS's desire to kill Chell. After destroying each detached Core one-by-one, Chell destroys the final Core (the Anger Core), and GLaDOS is sent literally spiraling into her demise, as the destruction of her generators triggers a gravitational vortex, which deposits Chell on the surface.
Chell slowly regains consciousness in the parking lot of the Enrichment Center, with with a lifeless GLaDOS beside her. As Chell's vision clears, the Party Escort Bot thanks her for "assuming the party escort submission position", and begins dragging her back into the now-ruined Aperture Science Facility. As Chell is dragged away, it is revealed that the destruction of the Central Core (GLaDOS) resulted in the automatic activation of other Personality Cores, tasked with the management of the Enrichment Center while GLaDOS is offline. The final scene depicts the Companion Cube and a cake deep within the bowels Facility, waiting for Chell to claim them.
During the course of the comic, we are introduced to former Aperture scientist, Doug Rattman. He witnesses the apparent destruction of GLaDOS, and later, after escaping from the facility himself, witnesses the recapturing of Chell by the Party Escort Robot. Following the robot, he finds that Chell has been placed into an Extended Relaxation Vault. However, as a result of the explosion at the conclusion of Portal, all of the relaxation vaults' life support systems are offline. Doug patches Chell's vault onto a reserve grid (as he was unable to open the vault), allowing Chell to survive the years prior to her reawakening in Portal 2.
Many years after the events of the original games, Chell is revived by Wheatley, a Personality Core. After a brief introduction, he convinces Chell to escape with him from the ruined facility. The pair eventually find themselves in the remains of GLaDOS' chamber. Wheatley then inadvertently reawakens GLaDOS, who immediately recognizes Chell. Discarding Wheatley, GLaDOS plunges Chell back into the depths of Aperture, to resume testing.
Chell finds herself testing in the ruined facility with GLaDOS, but after several chambers, Wheatley rescues Chell to help him sabotage GLaDOS' weaponry, allowing for a coup to take place later. GLaDOS eventually manages to trap Chell and bring her into her lair. After finding that her preferred methods of murder are unusable, Chell and GLaDOS find themselves at a standstill. Wheatley reappears, and after Chell initiates a core transfer, replaces GLaDOS as the Central AI of Aperture. However, he goes mad with power, dismantles the remains of GLaDOS' head and reconfigures it into a potato battery, and accidentally sends both GLaDOS and Chell to the decomposing underbelly of the facility, "Old Aperture," which had been sealed off for many decades.
In Old Aperture, Chell is introduced to Cave Johnson, the now-deceased founder and CEO of Aperture and his assistant Caroline. Throughout the tests, Chell finds and re-activates the Repulsion, Propulsion and Conversion Gels. She is reunited with GLaDOS during her travel through Old Aperture, and the two forge a plot to overthrow Wheatley in exchange for Chell's freedom.
After departing from Old Aperture, the duo locate a test chamber that Wheatley is overseeing and attempt to disable him via a logical paradox. This fails, however, and they quickly find themselves solving Wheatley's own cobbled-together tests. Much like in the first game, Wheatley tries to kill Chell and GLaDOS, saying that he had found the perfect replacements for Chell. After a lengthy chase through the upper facility, Chell and GLaDOS are again in the Central AI Chamber with Wheatley. Chell furthers Wheatley's "corruption" by attaching corrupted cores to his frame, allowing for a second core transfer. Before Chell can do this, however, Wheatley detonates bombs that he had "booby-trapped the stalemate button" with in a last ditch effort to maintain control. However, Chell fires one last set of portals above and below Wheatley. These portals link together the Moon and the Central AI Chamber, and both Chell and Wheatley are sucked through into outer space. Seconds afterward, GLaDOS regains control of her chassis, rescues Chell, and closes the portals, leaving Wheatley to be lost in space. After a monologue, GLaDOS (supposedly) makes good on her promise, and delivers Chell, via high-speed elevator, to the surface above Aperture Science. As the elevator ascends, it enters an ampitheatre-like space, where a choir of turrets sing a farewell song to Chell. Chell's elevator emerges in a shed in a large field of wheat. Chell's Companion Cube is also sent up moments afterword, presumably as a token of "thank you" from GLaDOS. After expelling the Companion Cube, the elevator door slams violently, probably to indicate that GLaDOS does not want Chell to return to the Enrichment Center again.