In the bustling heart of New York City, high-strung equity trader Joy Ellis McNally (Cameron Diaz) faces a crushing blow when her fiancé dumps her during a surprise birthday party that is meant to celebrate him, a decision fueled by her uptight demeanor. Simultaneously, easy-going carpenter Jack Fuller (Ashton Kutcher) finds himself ousted from his job by his own father, Jack Sr. (played by Treat Williams). With both feeling vulnerably heartbroken, they embark on a wild escape to Las Vegas, accompanied by their supportive friends — Toni "Tipper" Saxon (Lake Bell), a vivacious bartender, and Jeff "Hater" Lewis (Rob Corddry), an ambitious lawyer.
In a twist of fate, Joy and Jack end up in the same hotel room thanks to a hotel mix-up. After resolving the confusion and enjoying the perks of upgraded rooms and club coupons, they indulge in a night of partying that culminates in an impulsive wedding. The next morning, however, reality sets in as they recognize the folly of their drunken nuptials and mutually agree to seek a divorce.
Before they finalize their decision, Jack tries his luck with a quarter Joy gives him at a slot machine and miraculously lands a three million dollar jackpot. Joy reminds him of their marital bond, asserting her claim to half of the winnings. Returning to New York, they head to court to dissolve their marriage, only to discover a judge's ruling stipulating that they must live together for six months while attending sessions with a marriage counselor, Dr. Twitchell (Queen Latifah). This arrangement aims to ensure they genuinely attempt their marriage. If either of them decides to bail without trying, the massive financial prize will be subjected to legal disputes.
Throughout this forced cohabitation, both Joy and Jack hatch clever plans to get the other to initiate the divorce. For instance, Jack deceitfully informs Joy that their counseling session has been canceled, and Joy retaliates by inviting female acquaintances to their home, hoping to provoke Jack into infidelity. Unexpectedly, their time together during Joy's job retreat leads them to rediscover their liking for one another, revealing that they might be better together than apart.
As the saga progresses toward a fateful court hearing about the $1.4 million (after taxes and their respective expenses), Joy encounters her ex-fiancé Mason (Jason Sudeikis), who offers her the engagement ring back, claiming she is still worth his time. Realizing Jack may have orchestrated this scenario to prompt her to cheat in order to move ahead with their divorce, Joy rebuffs Mason and heads decisively into court.
At the hearing, their counselor attests to their sincere efforts. The judge, instead of simply dividing the money, ultimately decides to split it while Joy declines to take any share. She even hands the engagement ring back to Jack, signifying her desire for a clean break. Triumphantly, she receives a promotion she's long coveted at work but chooses to turn it down, preferring to cultivate happiness over professional success.
In a stroke of realization, Jack’s parents note the budding romance between him and Joy, prompting him to seek her out. Tipper reveals Joy's whereabouts, leading him to a serene beach that Joy cherishes. There, in a heartfelt moment, Jack proposes to Joy once more, and this time, she joyfully accepts.
As the credits roll, viewers are treated to delightful scenes from their wedding day, alongside more antics involving Tipper, Hater, and a comical revenge plot against Mason, punctuated by a memorable moment where Hater skillfully cuts off Dave.
