[2] Cullen entered into the public eye in 1987 as a member of musical comedy group Corky and the Juice Pigs.

Corky and the Juice Pigs toured the world, winning awards at the Edinburgh Fringe & performing at Just for Laughs in Montreal eight times.

He wrote and mounted his own one-man show called Wood, Cheese and Children which went on to become a special in CTV's Comedy Now!

He has also won awards in 2001 for his gala performance at Just for Laughs, and in 2006 for hosting What Were They Thinking?, a CTV program in which Cullen visited various unusual and somewhat inexplicable landmarks around Canada.

On the Barenaked Ladies' 2004 U.S. and Canadian holiday tour, Cullen joined the band on the road.

He would tell a comedic version of the nativity story and sing Christmas songs with band member Kevin Hearn accompanying him.

[citation needed] In the 2010 and 2011 season of the Stratford Festival, Sean played Smee in Peter Pan, Pseudolus in A Funny Thing Happened on the Way to the Forum and Vinnie in The King of Thieves by George F. Walker.

[citation needed] From 2011 to 2020, Cullen hosted the podcast The Seánpod, featuring interviews with guests including Alan Thicke, Norm Macdonald and Doug Benson.

As of 2012 Cullen was a staple character and a frequent panelist on the Canadian version of Match Game which aired on The Comedy Network, and on The Debaters on CBC Radio.

Unnatural Acts was a television comedy filmed in 1998 which was written by and starring Cullen as well as future The Mighty Boosh actors Rich Fulcher, Julian Barratt, and Noel Fielding.

The show consisted of Cullen giving commentary and conducting interviews interspersed with musical selections.

Typical music selections included the likes of The Tragically Hip, Weakerthans, Tom Waits, and R.E.M.

[10] The series is a comedic take on reality television travel shows, on which comedians from two different countries debate the merits of their nations in a lighthearted manner.

Cullen co-hosts with New Zealand comedian Jarred Christmas, exploring the best examples of each episode's theme, before asking the viewers to vote for which nation is the best on the series' website.