McGrath started his career as a TV producer at the educational network TVOntario. In 1993, he was hired by Moses Znaimer and went to work at Toronto's groundbreaking Citytv station. As a producer on the Gemini Award-winning MediaTelevision, McGrath made the program on the intersection of digital culture and marketing one of the first in Canada to maintain an email address. Between 1993 and 1997, he did over five hundred stories on the first wave of dot.com entrepreneurs and visionaries, interviewing new media luminaries such as John Perry Barlow, Bruce Sterling, Peter Gabriel, and Nicholas Negroponte, as well as authors and TV types from P. J. O'Rourke to Chris Carter.
In 1997, McGrath signed on as the first producer for Space: The Imagination Station, Canada's Sci-Fi channel. There, he pioneered several of the station's early program segments, including a recurring comedy segment called "Conspiracy Guy". He also created and hosted the show's late-night movie show, Spacebar.
In late 2000, McGrath left Space: The Imagination Station to become a resident of the Canadian Film Centre's Prime Time TV program.
On August 26, 2008, Across the River to Motor City received seven Gemini Award nominations. McGrath was nominated for Best Dramatic Writing in a Miniseries, along with Bob Wertheimer and Jocelyn Cornforth.
In 2002, on a lark, McGrath wrote the book and lyrics for a satirical musical based on the movie Top Gun. Top Gun! The Musical became the highest grossing show in the history of the Toronto Fringe Festival. It was remounted in a successful commercial production at the Factory Theatre in June 2003, and was nominated for two Dora Mavor Moore Award for Best Musical and Best Leading Performance Male, Dmitry Chepovetsky.
Top Gun! The Musical has received several productions, in Texas and Halifax, N.S. In 2004, the original cast and creative team, led by Director Colin Viebrock, producer Derrick Chua, and writers Denis McGrath and Scott White took the show to the inaugural New York Musical Festival.
McGrath has also written several other plays, including Press'd, American Without Tears, and Pavlov's Brother (based on a New Yorker article by Andy Borowitz), co-written with Flashpoint co-creator Mark Ellis.
Flight of the Storks (2012)
XIII: The Series (2011)
Stargate Universe (2010)
The Border (2007–2008)
Blood Ties (2007)
Across the River to Motor City(2006)
Charlie Jade (2004)
In August 2005, McGrath started a blog called "Dead Things on Sticks." Initially a personal screenwriting blog, the site soon morphed into a much-read daily discussion covering the Canadian Television industry. McGrath appeared on a TV critics' panel at the 2007 Banff Television Festival along with Entertainment Weekly's Gillian Flynn, Bill Carter of the New York Times, and John Doyle, Television Critic for the Globe & Mail.
In 2007, in an article criticizing the lack of discerning Canadian TV criticism, Doyle wrote that "McGrath's site is thoughtful, learned and provocative about creating Canadian TV."
"Dead Things on Sticks" ceased regular updating in June, 2010. The archive, including McGrath's most popular craft posts, remain online.
- "TG!TM: Top Gun! The Musical". Retrieved 16 September 2014.
- "Your Media: Preserve Freedom, Diversity, Independence". Retrieved 16 September 2014.