Gregg has been in various productions with The Public Theatre, Manhattan Theatre Club, New York Theatre Workshop, Williamstown Theatre Festival, The Huntington, Woolly Mammoth and The Kennedy Center. He received a Lucille Lortel Award (Best Featured Actor) for his work in the Pulitzer Prize-winning play, Cost Of Living by Martyna Majok. He was nominated for a Drama League Distinguished Performance Award for the role of Richard in Teenage Dick by Michael Lew. Gregg is the founder and Artistic Director of The Apothetae, a theatre company dedicated to the production of works that explore and illuminate the “Disabled Experience.”