Brighton is the only son of Maxwell and Sara Sheffield. Because both his older and younger siblings are sisters, he feels like he is left out of the loop often. Thus, he squabbles with both of them, mainly his older sister, Maggie. He was often causing trouble for his sisters. Despite this, he was also very sensitive, and was very bitter in the beginning about his non-existent family (his father was always working, his mother was dead and his only siblings were girls), and once said "Won't we have to be a family first?" in response to Fran's enthusiasm for his school's carnival held for the students' families.
When the new Nanny, Fran Fine came along, Brighton knew not what to make of things at first. He wanted to hate her as he hated all his previous nannies, but he found that he liked Fran's down-to-earth and witty personality. He wasn't as expressive in his bond with her as his sisters, but looks up to Fran as his example. He tried smoking cigarettes once when Fran and her best friend Val mentioned that one of the very bad boys in their high school smoked heavily and was considered a god, yet, though he tried to blackmail Fran into not handing his father the headmaster's note about being caught smoking, he did nothing to Fran when she finally confessed the whole incident to Maxwell, leading his father to believe that Brighton actually likes Fran and doesn't want to see her gone, as no one (and certainly not one of the nannies) could control Brighton except his mother Sara because he feared her. He was also the person, after his father, who was most worried when Fran started dating in Season 1 that she'll leave the Sheffield home soon. This was especially obvious when he and his father fell asleep on the living room couches waiting for Fran to come back from her date.
Brighton's ambition was to become a Broadway producer, like his father. Also, he is insatiably girl crazy, and while his father thinks that is what boys are like, Fran doesn't approve of it at all. When Fran took a job on a soap opera in place of her long-time arch-rival, Heather Biblow, Heather was then given Fran's job as a trick to get Fran back. Brighton really liked her, (that is to say, he lusted after her) but his sisters, who sided with Fran, naturally, hated her; eventually Fran came back to her job, one of the rare occasions that she had the upper hand against her rival, and Heather was fired. Maggie, Fran and Gracie were exultant; Brighton walked around with the towel Heather wore in the episode wrapped around him, sobbing into it.
Brighton also joined a Canasta league which allowed him to bond with his soon-to-be grandmother, Sylvia Fine and his soon-to-be great grandmother, Yetta Rosenberg.
During the later seasons, Brighton seemed to obsess a lot about his trust fund, or possible lack of one. When anyone says he has lost his trust fund, he goes into a real state of shock.
Brighton was present during the spontaneous marriage of Niles and C.C., as well as the birth of his twin siblings, Eve and Jonah Sheffield.
At the show's end, he was accepted into Harvard University, but chose to take a year off to travel France and supposedly work as a mime. In the final episode he is shown taking a plane to France, and asked his sister Maggie to come with him to France, because he was "afraid of the Paris People!".