Shannon will join Michael Pitt, Steve Nuscemi and Kelly Macdonald in the pilot, which is based on Nelson Johnson's chronicle of the growth of Atlantic City in the 1920s. "Boardwalk Empire" was adapted for the small screen by "Sopranos" veteran Terrence Winter.
Pitt plays Jimmy Darmody, a young man who returns from World War I and puts his ruthless nature to the test as a flunky for Buscemi's Nucky Johnson, a businessman and Prohibition rum runner.
According to The Hollywood Reporter, Shannon will play Van Alden, a senior Treasury agent looking to crack down on Prohibition era bootlegging.
The trade paper also adds that Vincent Piazza ("The Sopranos," "Rescue Me") will play a young Lucky Luciano.
Shannon recently popped up at the Sundance Film Festival in "The Greatest" and "The Missing Person." His earlier credits include "World Trade Center" and "Bug."