C.J., a Catholic, is originally from Dayton, Ohio. Her father, Talmidge Cregg, was a math teacher at a local high school. Her mother had died some time ago and Talmidge subsequently remarried twice, most recently a fellow teacher named Molly. C.J. also has at least two older brothers, one of whom has a teenage daughter named Hogan (whose name is the result of the brothers being "golf-crazies"). She is over six feet tall, towering over most of the other members of the cast.
A National Merit Scholar, C.J. earned a master's degree in political science from the University of California, Berkeley; her undergraduate major and institution have never been disclosed. She was making $550,000 a year for her work at Triton Day, a prominent California public relations firm, before coming to work for Bartlet's 1998 presidential campaign for $600 a week ($31,200 a year). Coincidentally, she was fired from that job on the same day that Toby Ziegler came to California to ask her to join the Bartlet campaign; Leo McGarry was impressed by the work C.J. had done at EMILY's List. As White House Press Secretary, C.J. was sharp, well-spoken and witty. She was less than pleased to discover that her Secret Service codename was "Flamingo", a bird which C.J. described as being "ridiculous-looking". On festive occasions, C.J. can be persuaded to perform her dead-on lip synch of "The Jackal" by Ronny Jordan; this was originally Allison Janney's party piece, which was written into the series by Aaron Sorkin.
During the third season, C.J. received a series of death threats, which led to her being placed under the protection of Secret Service agent Simon Donovan (played by Mark Harmon), with whom she became romantically involved. Shortly after going off-duty, Donovan was shot and killed after becoming caught up in the armed robbery of a New York City grocery store in the episode "Posse Comitatus". C.J. has also had a long on-again, off-again relationship with The Washington Post's White House correspondent Danny Concannon, although C.J. felt that they could not date because it would be a conflict of interest. In the 7th season many references were made to their dating. During the first episode of the 7th season, the show flash forwards to the opening of the Bartlet Presidential Library, it was revealed that Danny and C.J. marry, and will have a child.
In the fifth season, it is revealed that C.J. had a one-night stand with Vice President John Hoynes, who was married at the time, approximately four years before the Bartlet Administration entered the White House. She tells Toby that she considers that night to be one of the greatest mistakes of her life. This past history is foreshadowed a few times in the series, years before the revelation. Also, during the fifth season episode "Access", it is stated that C.J. remains the only woman to have served two terms as press secretary. It is unclear if this is meant to be two full terms or reflects her real situation of serving one full term and half of another.
C.J. succeeded Leo McGarry as White House Chief of Staff in the sixth season (halfway through Bartlet's second term) after McGarry suffered a heart attack at Camp David. There has never been a female White House Chief of Staff in the real U.S. Government -- it is unknown if the same was true in The West Wing fictional universe. It would also be the first time any press secretary was elevated to the position. While her subsequent performance as the Chief of Staff appears at first to be procedural in nature and lacking the independent advice which Leo McGarry brought to the position, C.J. grows into the position. By the seventh season she is as confident with her new role as she was with her old, and has learnt to gauge the President's mood and when he will be most receptive of her ideas. C.J. was at first criticized on her appointment to the position of Chief of Staff because of her relative lack of Foreign Policy experience. However, during Season 7 she successfully navigates the murky waters of UN politics, setting up a UN Security Council resolution to end the (real-life) humanitarian crisis in Darfur, Sudan. She was recommended by Leo himself, giving the President a list of "just one name".
After the election of Matthew Santos as President of the United States, C.J. is offered any position she wants in the incoming Santos Administration by Chief of Staff-designate Josh Lyman and later offered by President-elect Santos a job as Senior Counselor to the President. This is only one of many job offers she receives, having already been offered several positions in the private sector, notably an offer by Frank Hollis (a Bill Gates/Ted Turner-like character) to manage a new $10 billion charitable organization. Her response to Hollis on how to spend his money best was to start by building proper roads in Africa in order to make it easier to get food and services to people in need and if there was money left over to start on the plumbing. She felt obligated to take the position in the Santos Administration, but was convinced by Danny Concannon to do what she wanted, which was to take the Hollis job.
In the opening episode of the final season a flash-forward to the time of the dedication of the Bartlet presidential library, three years after the end of his presidency, it is revealed that C.J. lives in Santa Monica, California with husband Danny Concannon and their child.