The drama focuses on a group of young people working in Washington.
TV Line says that Zegers, who plays Damien in Gossip Girl, has now joined the cast as Monty.
Monty is described as a wealthy young stockbroker from a well-connected family. He is thought to be an old rival of Presidential speechwriter Andrew Pierce, played by James Wolk.
Georgetown, which will be produced by Gossip Girl showrunners Josh Schwartz and Stephanie Savage, will also star Joe Mazello, Condola Rashad, Katie Cassidy and Daisy Betts.