How to Murder Your Life

Marnell grows up in Washington, D.C.. Her father is an abusive and controlling psychiatrist who eventually has her older sister sent to the reform school Cross Creek Manor where her movements are severely restricted. To escape her father's rages Marnell asks to attend boarding school and is sent to Lawrence Academy. After recreationally taking Ritalin Marnell believes she has ADHD. Her father prescribes the drug to her and Marnell begins to use it both as a study aid and recreationally. In her final year of school Marnell discovers she is pregnant and delays having an abortion for so long that she enters her second trimester of pregnancy. After being accepted to Bard College in 2000, she harasses other accepted students online leading to her expulsion from Lawrence Academy, the rescission of her Bard acceptance, and the revelation of her pregnancy to her parents. Her mother takes her for an abortion which Marnell finds traumatizing.

Marnell applies to and gets into an acting class in New York City but finds the workshops boring and is unable to make friends. Alone and isolated she develops bulimia. While attending a show at the Comedy Cellar she meets and is picked up by Ardie Fuqua who helps to introduce her to NYC nightlife. Marnell spends the next few years developing a drug habit, dropping in and out of colleges, and building contacts in the entertainment and fashion worlds.

At 21 she works in the closet at Vanity Fair. This gives her a taste for magazine journalism and she uses her connections to nab an internship at Nylon where she works for beauty editor Charlotte Rudge. She subsequently gets internships at Teen Vogue and Glamour. After getting a free copy of Jean Godfrey-June's memoir she becomes obsessed with the beauty editor and eventually lands a job as her assistant. Marnell works well with Godfrey-June and finds herself enjoying the perks of working at Lucky magazine. However, after moving into a new apartment that is infested with mice she begins to take more drugs to cope with the infestation which leads to further paranoia. She eventually contacts her parents to tell them she believes she is addicted to Adderall. They take her to a psychiatrist who encourages Marnell to go to rehab. Marnell explains her addiction to Godfrey-June, who assures her she will have a job when she returns, and goes to the Silver Hill Hospital. Upon returning Marnell is able to keep sober for a few months before she begins to abuse alcohol and then returns to abusing Adderall. During the Great Recession, her co-worker is fired while Marnell is officially promoted to associate Beauty Editor. Marnell immediately abuses her privileges as Beauty Editor but is protected from consequences by her intern, her good relationship with Jean Godfrey-June, and PR reps who are more interested in preserving their relationship with her magazine then in checking her behaviour.

Marnell becomes a roommate of Nev Schulman. This coincides with the worst of her drug abuse as her only friend, a fellow junkie named Marco, encourages Marnell to do harder drugs and becomes increasingly abusive and threatening towards her, repeatedly breaking into her home and robbing her. Eventually Marco destroys Schulman's apartment, causing her to be evicted. In 2009, on her 27th birthday Marnell realizes she has no friends and no one to spend the day with. Shortly after she reconnects with Marco who steals her keys and robs her entire apartment. Tracking his movements she is able to successfully recover her things and also realizes he had been robbing her for years before she noticed. After this breakdown her father and Jean Godfrey-June try convince her to go to rehab a second time. Instead, Marnell goes to a mental institution, claiming to be suicidal, as she wants to keep up the fiction that she is sober. Her doctor at the mental institution eventually persuades her to go to rehab, but Marnell leaves after nine days. She returns to drugs and to her job at Lucky. However she is no longer able to perform many of her job responsibilities and despite support from the staff she ultimately decides to quit.

During her unemployment Marnell attempts suicide. After being cut off from the rest of her family she turns to her wealthy grandmother, Mimi, who pays off her debts and allows her to stay with her in Charlottesville, Virginia. Marnell eventually returns to New York and splits her time between that city, where she spends her time partying with graffiti artists and drug users, and Charlottesville. When Jane Pratt launches the online magazine xoJane in 2011 Marnell's friend, Lesley Arfin, encourages her to apply. Marnell is hired and while there works on health, beauty and drugs, finally able to write openly about her experiences as an addict.

Marnell disdains of the online publication, nevertheless her columns are successful. After Whitney Houston dies in early 2012, Marnell writes about life as a woman who is a drug addict and the piece goes viral leading her to negotiate a raise with xoJane. Shortly after she is pushed into rehab by her work and shortly after, still on drugs and unable to maintain her work, Marnell leaves the publication. Nevertheless, in a series of interviews she gives about being a drug addict her popularity rises. She is able to negotiate a well paying job at Vice and obtain a literary agent though it takes her till 2013 to piece together a coherent book proposal.

In an afterword Marnell claims to be doing much better, saying she is much closer with her family, but also admits to still abusing drugs.

Marnell's memoir was warmly received. The Globe and Mail praised her "chic-macabre sense of humour".[2] Anne Helen Petersen writing for The New York Times review praised her for keeping a balance "between glamorizing her own despair and rendering it with savage honesty."[3]

The Irish Times however criticized the memoir saying that Cat Marnell was always playing the persona of Cat Marnell and suggested "she can do much better".[4]