In 1975, Palillo was cast as Arnold Horshack, one of the misfit "sweathogs" in the high school sitcom Welcome Back, Kotter, whose antics made him one of the stand-out characters of the series.
In the last season of the series, a backdoor pilot episode for a spin-off series featuring Horshack was produced, but the series was not developed.

Following Kotter, Palillo appeared in leading and supporting roles in various television series and films.
He voiced characters on such animated series as Laverne & Shirley in the Army, Darkwing Duck, and Rubik, the Amazing Cube, in which he played the lead character.
In 1996, Palillo played himself in several episodes of the television sitcom Ellen, playing the love interest of Ellen's friend Audrey.
Palillo also spent a year on the daytime show One Life to Live and also acted in Friday the 13th Part VI: Jason Lives (1986), and the lead in The Curse of Micah Rood.

He returned to New York in 1991, and played such roles as Mozart in Amadeus and regionally as George in Who's Afraid of Virginia Woolf?,
Arthur in Camelot and Nathan Detroit in Guys and Dolls.
He appeared on Broadway in 2008 in Broadway Backwards 4, a charity event benefiting Broadway Cares/Equity Fights AIDS and The Lesbian, Gay, Bisexual & Transgender Community Center.
Among his other New York City credits were a one-person show in 2000 where he portrayed Nazi criminal Adolf Eichmann in The Diary of Adolf Eichmann off-Broadway.
Palillo, in a newspaper interview in 1997, said he lamented his role as Horshack as he was permanently typecast, which he believed had damaged his career.

As a director, Palillo directed successful productions of the musical Three Guys Naked From The Waist Down in Los Angeles, A Closer Walk with Patsy Cline, and a new edition of Phantom Of The Opera at the Cuillo Center for the Arts in West Palm Beach, Florida.
In 2007, he introduced a clothing line specializing in limited-edition T-shirts produced by Rotter and Friends.
Palillo was also an artist, providing artwork for two children's books, The Red Wings of Christmas and A Gift for the Contessa.

In 2005, his first full-length play The Lost Boy, the true story of Peter Pan author J. M. Barrie, premiered at the Helen Hayes Theatre in Nyack, New York, and later played at the Queens Theatre in the Park in Queens, New York and at the Eldorado's Springs High School in Eldorado Springs, Missouri.

He taught freshman drama at G-Star School Of The Arts for Motion Pictures and Broadcasting in Palm Springs, Florida.
In 1975, Palillo was cast as Arnold Horshack, one of the misfit "sweathogs" in the high school sitcom Welcome Back, Kotter, whose antics made him one of the stand-out characters of the series. In the last season of the series, a backdoor pilot episode for a spin-off series featuring Horshack was produced, but the series was not developed.
Following Kotter, Palillo appeared in leading and supporting roles in various television series and films. He voiced characters on such animated series as Laverne & Shirley in the Army, Darkwing Duck, and Rubik, the Amazing Cube, in which he played the lead character. In 1996, Palillo played himself in several episodes of the television sitcom Ellen, playing the love interest of Ellen's friend Audrey. Palillo also spent a year on the daytime show One Life to Live and also acted in Friday the 13th Part VI: Jason Lives (1986), and the lead in The Curse of Micah Rood.
He returned to New York in 1991, and played such roles as Mozart in Amadeus and regionally as George in Who's Afraid of Virginia Woolf?, Arthur in Camelot and Nathan Detroit in Guys and Dolls. He appeared on Broadway in 2008 in Broadway Backwards 4, a charity event benefiting Broadway Cares/Equity Fights AIDS and The Lesbian, Gay, Bisexual & Transgender Community Center. Among his other New York City credits were a one-person show in 2000 where he portrayed Nazi criminal Adolf Eichmann in The Diary of Adolf Eichmann off-Broadway. Palillo, in a newspaper interview in 1997, said he lamented his role as Horshack as he was permanently typecast, which he believed had damaged his career.
As a director, Palillo directed successful productions of the musical Three Guys Naked From The Waist Down in Los Angeles, A Closer Walk with Patsy Cline, and a new edition of Phantom Of The Opera at the Cuillo Center for the Arts in West Palm Beach, Florida. In 2007, he introduced a clothing line specializing in limited-edition T-shirts produced by Rotter and Friends. Palillo was also an artist, providing artwork for two children's books, The Red Wings of Christmas and A Gift for the Contessa. 
In 2005, his first full-length play The Lost Boy, the true story of Peter Pan author J. M. Barrie, premiered at the Helen Hayes Theatre in Nyack, New York, and later played at the Queens Theatre in the Park in Queens, New York and at the Eldorado's Springs High School in Eldorado Springs, Missouri.
He taught freshman drama at G-Star School Of The Arts for Motion Pictures and Broadcasting in Palm Springs, Florida.
Ron Palillo