Novello is best known for his work on NBC's Saturday Night Live, from 1977 until 1980, and then 1985 until 1986, as the character "Father Guido Sarducci".

Novello has appeared as "Sarducci" on many television shows since then, including Married... with Children, Blossom, It's Garry Shandling's Show, and Square Pegs.

Novello made newspapers around the world when he visited the Vatican in 1981 wearing the full Father Guido Sarducci costume and, while taking photographs in an area where photography was prohibited, was arrested by the Swiss Guards, and eventually charged with "impersonating a priest". The charges were later dropped.

Novello started his career as a performer on The Smothers Brothers Show in 1965.

In the early 1980s, Novello produced SCTV, a Toronto-based comedy show, which starred Martin Short, Joe Flaherty, John Candy, Eugene Levy, Andrea Martin, and Catherine O'Hara.

In the 1970s Novello started to write letters to famous people under the pen name of Lazlo Toth (name taken from that of a deranged man who vandalized Michelangelo's Pietà in Rome). The letters, designed to tweak the noses of politicians and corporations, were full of deliberate misstatements of fact and inside jokes. Many of these letters received serious responses; Novello sometimes continued the charade correspondence at length, with humorous results. The letters and responses were published in the books The Lazlo Letters (ISBN 1563052857), Citizen Lazlo! (ISBN 1563051826), and From Bush to Bush: The Lazlo Toth Letters (ISBN 0743251083).

In 1984 Novello wrote "The Blade," a high school yearbook parody in which the students are represented by sheep.

Novello co-wrote the unfilmed script for "Noble Rot", with John Belushi.

In 1990, Novello portrayed "Dominic Abbandando" in the film, "Godfather: Part III".

In 2003, he filed papers to enter the 2003 California recall election, but failed to collect enough valid signatures to qualify for the ballot.

In 2005, after the death of Pope John Paul II, Novello, as Father Guido Sarducci, reprised his former SNL role as "Special Vatican Reporter" for Air America Radio host (and fellow "Saturday Night Live" alumnus) Al Franken. He continued this role until the election of Pope Benedict XVI.

Don Novello currently resides in Marin County, California.

His sister-in-law Antonia Novello was Surgeon General of the U.S. from 1990 to 1993.