In New York City in a Local Brooklyn Fire Station, there are lots of firefighters. Charles 'Chuck' Levine (Who is a chronic womanizer) and Lawrence 'Larry' Valentine (Who is a bachelor and trying to raise his children after his wife passed away some time ago) are two veteran New York City Firefighters. During a routine sweep of a burned building, a segment of floor collapses and Chuck almost dies. Larry rescues Chuck by shielding him from the falling debris. As he and Larry awaken at a hospital later, Chuck vows to repay his debt in any way possible. The incident prompts Larry to realize the fact that death can come for him at any moment, but he has difficulties naming his children as primary beneficiaries in his life insurance policy. Larry was given at least a year to change his beneficiaries but he was profusely mourning his wife, and left it too late. However, One of the ways suggested for him to do so is to get married. Inspired by a newspaper article about domestic partnerships, Larry asks Chuck to enter a civil union with him. Although at first Chuck declines, he is reminded of his debt to Larry and finally agrees.
Chuck and Larry become domestic partners and Chuck becomes Larry's primary beneficiary in the event of his death. Soon, New York City investigators arrive to inquire about their partnership. They lie to the investigator by saying that they are really in love with each other and insist they've been having "Loads of Sex, Gay-crazy sex, Man on Man, Loving Every Minute". Chuck and Larry then decide to enlist the help of a lawyer, Alex McDonough, who suggests that they get married. Chuck and Larry then marry in Canada and move in together. When they get married in Canada, the Asian minister who proclaims "I Now Pronounce You, 'Husband and Husband, You May Now Kiss The Husband" is shocked to see Chuck and Larry slap each other the cheek (as opposed to kissing) when ordered to "Kiss the Husband". Chuck and Larry then retort by saying "That's How We Roll In Our House, Baby".
On the first night of Chuck living with Larry and his kids, Chuck insists on sleeping in Larry's bed next to him much to Larry's objection that he could not stand the thought of someone other than his wife Paula sleeping beside him but Chuck, insisting they are on honeymoon, refuses to budge. Eventually Larry gives in and lets Chuck sleep there just as long as Chuck does not make silly voices to Larry about betrayal. The next day, the kids wake up both Chuck and Larry and the maid Theresa who had claimed she'd been cleaning the bed making Chuck and Larry both jump and scream in fright.
When another investigator, Clint Fitzer comes along, who inspects their garbage, Chuck and Larry get alarmed to discover that it wasn't gay enough, they rush to a nearby supermarket to get items of merchandise that are 'more gay'. There Chuck bumps into Alex, the lawyer, whose help they enlisted before getting married. She informs Chuck that she fell out of love with her boyfriend and broke up and tells him there is a gay benefit costume party later on that week.
At the gay benefit costume party, the party goers are confronted by homophobic protesters, whose leader, Jim the minister, calls Chuck a "faggot". Chuck punches him, causing the event to be published in a newspaper. With their apparent homosexuality and marriage revealed, the pair come under fire: Chuck and Larry are heckled, while their fellow FDNY firefighters refuse to work or even play basketball alongside the couple. Their only ally is Fred G. Duncan, an angry, intimidating firefighter who comes out to a very surprised Chuck.
Larry's effeminate son, Eric is harassed in school by a homophobic bully - but he surprises everybody by easily winning the fight. During the ordeal, the previously homophobic pair come to understand what it is like to be persecuted, and become more accepting of homosexuality. Chuck becomes romantically interested in Alex after the two spend time together, but finds himself unable to get close to her because she thinks he is gay. Meanwhile, Clint Fitzer arrives to investigate the couple. The strain on both Larry and Chuck leads to a verbal fight and also working different shifts, although there was a petition to have Chuck and Larry thrown out of the firehouse. This prompts Larry to confront the crew about their personal embarrassments on the job that Chuck and Larry helped them overcome. After this a call goes out and before they go on the call Larry even goes as far as to say: "Oh! A fire. I hope its not a big one because the faggot who's been saving your sorry asses thanks to you is on another shift". After Larry's shift is over, Chuck and Larry reconcile their differences.
The marriage soon comes under fire, as numerous women provide testimonies to having slept with Chuck in the recent past, and the couple is called into court to defend their marriage on charges of fraud. They are defended by Alex, and their fellow firefighters arrive in support, after they realize all Chuck and Larry have done for them over the years, and how they were treating Chuck and Larry. Fitzer interrogates both men, who testify that they genuinely love each other (albeit in a platonic fashion). As his final demand, Fitzer asks for the pair to kiss to prove that their relationship is physical, but before they do so, they are interrupted by Captain Phineas J. Tucker, who finally reveals that their marriage is a sham and that they are both straight He says "I'd Rather Change My Grandfather's Diapers Than See Two Straight Guys Kissing". Tucker attempts to save Chuck and Larry by claiming that he would have to be arrested as well, since he knew about the falsity, but failed to report it. This prompts the other firefighters to each claim a role in the wedding in a show of solidarity. However, Chuck, Larry, and the other firefighters are sent to jail "For Stealing From The City Of New York", but they are quickly released after negotiating a deal to provide photos for an AIDS research benefit calendar. The deal including pleading guilty to fraud, which would reduce the charges to a misdemeanor. Two months later, Duncan and Alex's brother, Kevin, are married in Canada at the same chapel as Chuck and Larry were. At the wedding party, Larry finally moves on after the death of his wife and talks to a new woman, while Alex tentatively agrees to a dance with Chuck. The film ends when Lance Bass sings, and little Eric tap-dances.