After graduating, in 1981’s Emerson Class, he took up a job at the same school to teach comedy writing and worked there for five years. Denis began his comedy career in the Boston comedy scene, an underground club. His first real gig was at the Rascals Comedy Club as part of the Television Show, The Rascals Comedy Hour, on October 18, 1990. He did local comedy series as well.
In 2009, Leary began the Rescue Me Comedy Tour in Atlantic City, New Jersey. Later, he played Captain George Stacy in the movie The Amazing Spiderman.
In 2008, he wrote a book Why We Suck: A Feel Good Guide to Staying Fat, Loud, Lazy and Stupid.
Leary met Ann when he was her instructor in an English class at Emerson College and started dating until the two got married. The family of Leary and Ann have two beautiful children, John Joseph a.k.a, Jack and Devin. The family leads a happy life together free from any dispute. Denis holds an impressive net worth which is estimated to be around $25 million funded by his standup career, book sales, and Comic DVD releases.