- Denis was inspired to try acting when one of his teachers persuaded him to perform in a school production.
- Denis has won a CableACE Award for Best Director of a comedy for Showtime's National Lampoon's Favorite Deadly Sins.
- Denis has appeared in TV commercials for IBM, Nike, MTV, Quaker State Motor Oil, Holsten Pils Lager and Boston radio station WAAF 107.3 FM.
- Denise has formed his own production company called 'Apostle'.
- Denis was the founder of Emerson Comedy Workshop. After graduating college, he briefly taught at the workshop.
- Denis' classmates at the Emerson College included Mario Cantone, Eddie Brill and Steven Wright.
- In 1996, Denis had a role in Beautiful Girls, but had to pull out due to scheduling conflicts.
- Denis is 6 feet (1.83 metres) tall.
- Denis was one of People magazine's Sexiest Men Alive, 2006. He is found in the "Sexy at every age, Age 49"
- Denis has released two comedy albums, No Cure for Cancer and Lock and Load.
- Denis' song A*shole was voted #1 in the Triple J Hottest 100 as well as reaching #2 in the singles chart in Australia.
- In 2004, Denis released the EP Merry F#%$in' Christmas, which included a mix of new music, previously unreleased recordings and a few tracks from Lock 'N Load.
- Denis has been married to Ann Lembeck since 1982. They have 2 children together, one of them being actor Jack Leary. Denis is also the cousin of Conan O'Brian and producer, Jane O'Brien.
- Denis follows the Boston Red Sox.
- Denis is a godparent of Damian Charles Bing, son of Elizabeth Hurley.
- Denis assisted during the collapse of the World Trade centre on September 11th, by getting behind the wheel of a fire engine when the New York Fire Department were short handed.
- Denis received both a Golden Globe nomination and a Best Actor in a Drama Series Emmy award in 2006 for his role in Rescue Me.
- Denis had a roast held in his honor at the New York Friar's Club in 2003. Jeff Garlin acted as the roastmaster, with roasters including Mario Cantone, Dane Cook, Lenny Clarke, Gina Gershon, Conan O'Brian, Colin Quinn, and Michael J. Fox.
- Denis founded the Leary Firefighters' Foundation charity in response to the Dec. 3, 1999 warehouse fire that killed six firefighters in his hometown of Worcester, MA. His cousin Jeremiah Lucey was among the six heroic firefighters killed. Denis also established a second division of LFFF, the Leary Firefighters' Foundation Fund for New York's Bravest in response to the FDNY's losses in the Sept. 11th attacks.
- Denis got an an Honorary Doctorate in Arts and Letters from Emerson College.
15 June 2005.
- Denis wanted to be an NHL star as a child.
- One of Denis' trademarks is to smoke cigarettes and drink beer during his routines.
- Denis: Why hate someone for the colour of their skin when there are much better reasons to hate them.
- Denis: Most movies suck, even the independent ones. Hollywood is like baseball - Hit three good ones out of 10 and you're in a Hall of Fame. I don't think like those guys who say, 'I'm hot again, so I've got to get back into a big movie.'
- Denis: The things that make me angry still make me angry. George Carlin is 67, and he's still as funny as he's ever been, and he's still angry. And that makes me feel good, because I feel like if I stick around long enough, I'll still be able to work.
- Denis: Did you ever notice they never take any fat hostages? You never see a guy coming out of Lebanon going: `I was held hostage for seven months and I lost 175 pounds, I feel good and I look good and I learned self-discipline. That's the important thing.'
- Denis: My biggest regret in life is that I didn't hit John Denver in the mouth while I had the chance.
