His roles on American television include Shane Donovan on the soap opera Days of Our Lives, Maxwell Sheffield on the sitcom The Nanny, and the voice of Dennis the Goldfish on Stanley for which he won a Daytime Emmy Award.

In 1996, Shaughnessy reunited with another Days of Our Lives co-star—Charlotte Ross, who portrayed Shane's daughter, Eve Donovan—in the TV movie A Kiss So Deadly.

He was also in the 2000 made-for-TV Halloween movie Mom's Got a Date with a Vampire starring Caroline Rhea; she guest-starred on The Nanny in 1998 as part of a cross-over with Hollywood Squares.

That same year, Shaughnessy made two appearances on The WB's Sabrina (starring Rhea, Melissa Joan Hart, and Beth Broderick), playing two different characters.

Shaughnessy appeared on an episode of NBC's Law & Order: Special Victims Unit and is also the voice of Dennis the Goldfish on the Disney Channel cartoon series Stanley.

Shaughnessy returned to Days of Our Lives in May 2010, in a storyline associated with the funeral of Alice Horton (played by Frances Reid), briefly reuniting him with his former co-star Patsy Pease (Kimberly).

In June 2011, Shaughnessy appeared as Henry Higgins in My Fair Lady at the North Shore Music Theatre in Beverly, Massachusetts, and returned there to play Georges in La Cage aux Folles in fall 2013 .

He made a guest appearance on the first-season finale of Fran Drescher's TV Land sitcom, Happily Divorced, first airing on 17 August 2011.

On 23 January 2014, it was announced that Shaughnessy would assume the lead role in the play Harvey at the New Theatre in Overland Park, Kansas, after original star Judge Reinhold was offered the opportunity to leave the production.

In August 2014, Shaughnessy made a guest appearance on the Disney Channel show Dog with a Blog as business tycoon Tom Fairbanks, a man who wanted to buy Stan, the title character, and use him as the spokes-dog for his animal rescue campaign.