The film opens with Ted (Seth MacFarlane) and Tami-Lynn (Jessica Barth) tying the knot, officiated by none other than Sam Jones (himself). The wedding reception reveals that John (Mark Wahlberg) is feeling down after his divorce from Lori six months earlier. Meanwhile, we learn that Guy (Patrick Warburton) is now dating Rick (Michael Dorn). A hilarious dance number by Ted on their giant wedding cake sets the tone for the movie.
Fast forward one year, Ted and Tami-Lynn’s romantic bliss has turned into financial stress as they struggle to make ends meet working as cashiers. While Ted is frustrated with Tami-Lynn's shopping habits, she is equally discontent with his spending on weed. In search of support, Ted meets John at McFeltys Pub, where a flirty bartender grabs John’s attention, but he remains uninterested. Seeking a free drink, Ted tries to convince the bartender to keep quiet about Jay Leno’s personal escapades, just moments before an embarrassed Leno rushes out of the bathroom.
During a routine day at the grocery store, Liam Neeson (himself) unexpectedly shows up to buy Trix cereal, having been led to believe it's only for children. Ted kindly assures him it’s perfectly acceptable. A coworker named Joy proposes that having a child could save Ted and Tami-Lynn's faltering marriage, leading Ted to suggest the idea to his wife, who enthusiastically agrees, believing she would make a wonderful mother.
After having a smoke and watching Law & Order with John, Ted shares his plan about becoming a parent and decides that Sam Jones, being a famous actor, could serve as a perfect sperm donor. However, their hopes are dashed when Sam reveals his sperm count is shockingly low due to past substance abuse. Desperate for a solution, the duo hatches a scheme to steal Tom Brady's (himself) sperm.
In an outrageous turn of events, John disguises himself as an A/C repairman to break into Brady's house. Their clumsy plan is derailed when Brady awakes, and they escape in a panic, with John feeling hurt that Ted didn’t consider him as a potential donor. A trip to a fertility clinic becomes chaotic as John finds himself covered in rejected sperm samples.
Realizing that Tami-Lynn is unable to conceive due to her past drug use, they try to adopt but face hurdles because Ted lacks legal personhood. Fired from his job and with their marriage annulled, John suggests they fight back with legal action. Luckily, they come across Samantha Louise Jackson (Amanda Seyfried), a bright yet laid-back lawyer who agrees to take their case pro bono.
A series of comedic montages follow as they dig through legal texts and bond over shared interests. Samantha introduces them to her favorite strain of weed, aptly named "Get Me Home," which leads to amusing interactions. During a sensitive moment while watching Roots, Ted realizes their struggle for identity is similar to the experiences portrayed in the film.
As they prepare to face a powerful legal team from Hasbro, Ted and his friends experience both highs and lows through a series of comedic events—including attending a chaotic Comicon where even more mischief unfolds. Ultimately, they lose their court case, but a spark of hope ignites when Patrick Meighan (to be revealed as Morgan Freeman), a prominent Civil Rights attorney, agrees to help after witnessing the emotions stirred by Johnny's brave actions.
A touching yet humorous road trip to New York unfolds with stops that lead to unexpected experiences and even budding romances among the group. Just when the situation looks bleak, sparks fly in an unexpected Comicon showdown, culminating in Ted’s daring escape from Donny (Giovanni Ribisi) and an emotional climax—only to discover that Johnny’s life hangs by a thread after a heroic effort at the event.
In a twist reminiscent of romantic comedies, Johnny reveals himself to be alive, bringing joy back to the group. Hope rekindles as Patrick decides to take on Ted’s case, ultimately leading to a triumphant courtroom victory that changes Ted's status forever. The story wraps up with Ted and Tami-Lynn adopting a child they name Apollo Creed Clubberlang, solidifying their unconventional yet loving family.
In a humorous post-credits scene, a disheveled Liam Neeson returns the Trix cereal to the store, leaving audiences in stitches.
