Cormac trained at Atlantic Theater Company in New York and was in the inaugural Atlantic Los Angeles class taught by David Mamet, Clark Gregg and Lee Cohn. He is an alum of the Upright Citizens Brigade Theater and has worked extensively with Bob Krakower as well.

In Television, he has appeared in Veep, The Blacklist, Blue Bloods, Believe, Person of Interest and It's Always Sunny in Philadelphia.

He has also performed in many of the off off Broadway houses in New York in shows including: Hell House (dir. Alex Timbers), I Was Tom Cruise (Outstanding Play, NY Fringe Festival), and The Girl in the Flammable Skirt (Ateh Theater Company) as well as a year run in The Third Degree at Upright Citizens Brigade, NY. Cormac has also done commercials for McDonalds, Wendys, Bud Lite, Fedex Kinko's, and Verizon.