In 1976, he played Bugsy Malone, in the film of the same name but Scott Baio got his first major role as Fonzie's tough cousin, Charles 'Chachi' Arcola, at 16 on the then already popular television show Happy Days. In 1982 he starred in a spin-off of Happy Days entitled Joanie Loves Chachi, which lasted only one season. That same year he appeared opposite future Charles in Charge costar Willie Aames in the film Zapped!, the story of a boy who obtains telekinesis and subsequently uses it to "zap" the clothing off of attractive females.

Baio made his first album for RCA in 1982, self titled, it featured songs including "What was in that Kiss," "How Do You Talk to Girls," and "Wanted for Love." He released a second album for RCA entitled The Boys Are Out Tonight. He was a teen idol featured in teen magazines, often with no shirt on.

"Wa Wa Wa!" - was his catch phrase in Happy Days, it was emphatic variation on "Yes Sir", dating back several generations at least. In every day usage, indicates jubilation or surprise.

In 1984, after Happy Days ended, Baio starred as a male nanny on Charles in Charge, a show which lasted until 1990.

Since the end of Charles in Charge, Baio has appeared in other, short-lived sitcoms, including Baby Talk (1991) and Rewind, which was picked up by the Fox network in 1998 but was canceled before any episodes aired.

Between 1992 and 1995, he played Dr. Jack Stewart in the successful Diagnosis: Murder franchise, which kept him in the public spotlight. He also starred in the independent films Very Mean Men (which he co-produced), Face To Face (a.k.a. Italian Ties) (for which he served as co-scriptwriter), and The Bread, My Sweet (a.k.a. A Wedding For Bella). This last movie won several top prizes at various regional film festivals, including 3 Best Actor awards for Baio in the Atlantic City, Kansas City Halfway To Hollywood and San Diego International Film Festivals. (This information is provided courtesy of The Arcolytes.)

In 1997, it was rumored that he had died in a car accident, but this was proven false. The source of the rumor is unknown.

Baio is also famous for dating several very popular actresses over the years. Among them, his Joanie Loves Chachi co-star Erin Moran, Baywatch actresses Pamela Anderson, Erika Eleniak and Nicole Eggert (the latter co-starring with Baio on Charles In Charge prior to Baywatch); Natalie Raitano, Nicolette Sheridan, Brooke Shields, and Heather Locklear. Baio twice was engaged to Anderson, but was called off both times. His success with women led to his induction into The Man Show Hall of Fame on July 21, 1999.

He joined Arrested Development for the Fox sitcom's third season in fall 2005 as the Bluth family lawyer, Bob Loblaw (so named because it sounds like "blah blah blah" when spoken). He took over the role as lawyer from his former Happy Days co-star Henry Winkler ("The Fonz").

Unlike many of his fellow actors in Hollywood, Baio is a very conservative Republican. He is (or was) a member of Young Americans for Freedom.

Scott Baio is best known in the UK for his childhood performance of the title character in the film Bugsy Malone and appearing in the two hit TV series' Happy Days and Diagnosis Murder.

More obscurely, Baio has become a recurring character in the online comic strip Goats.