Once upon a time, there was an infant named Norbit Albert Rice who was unceremoniously dropped off at the Golden Wonton Restaurant and Orphanage. Raised by Mr. Wong (EDDIE MURPHY), young Norbit's best friend was another orphan, Kate. But when she was adopted, he was all alone until the imposing Rasputia saved him from some bullies and declared him hers forever.
Years later, Norbit (EDDIE MURPHY) is the henpecked and mousey husband to Rasputia (EDDIE MURPHY), a mean and extremely obese woman who runs their Boiling Springs, Tennessee home with an iron fist. That traits run in her family as her three muscular brothers, Big Jack (TERRY CREWS), Earl (CLIFTON POWELL) and Blue (LESTER 'RASTA' SPEIGHT) use their Latimore Construction Company as a front for extorting all of the local businesses. The only people who don't kowtow to them are Mr. Wong as well as Pope Sweet Jesus (EDDIE GRIFFIN) and Lord Have Mercy (KATT WILLIAMS), two former pimps who now run the local ribs joint.
Working as their bookkeeper, Norbit isn't remotely happy there or at home, especially when he discovers that Rasputia is having an affair with local aerobics instructor Buster (MARLON WAYANS). Yet, things look up when Kate (THANDIE NEWTON) unexpectedly returns to town, hoping to purchase the orphanage from Mr. Wong. Norbit is excited to see his childhood friend now grown up and quite attractive, but is heartbroken when he learns she's engaged to real estate developer Deion Hughes (CUBA GOODING, JR.).
Nevertheless, he's pleased to spend time with her, something that doesn't set well with Rasputia. When Norbit learns that Deion is in cahoots with his in-laws to conspire against Kate and her plans, the mild-mannered man decides he must do something before it's too late, all while having to deal with his ill-tempered wife.