Dallas was born and raised in Houston, Texas, where he attended Paul Revere Middle School and Robert E. Lee High School. He then moved to Sarasota, Florida, where he graduated from Sarasota High School in 1988 and attended Manatee Community College. In 1990, Roberts was accepted to the Julliard School in New York City, New York, where he graduated in 1994 as a member of Drama Division's Group 23.
Roberts is primarily based in New York City, where he regularly appears in theatrical productions. Off-Broadway, he has appeared in a revival of Lanford Wilson's Burn This, Nocturne (which he was nominated for a Desk Award for), and Caryl Churchills A Number. He was slated to make his Broadway debut as Tom Wingfield in a revival of Tennessee Williams' The Glass Menagerie, but was replaced by Christian Slater during rehearsals.
His film work includes the screen adaptation of Michael Cunningham's A Home at the End of the World, Walk the Line, and The Notorious Bettie Page. He also had a regular role on the drama series The L Word. Roberts eventually became part of the AMC original series Rubicon, where he played Miles Fielder, a genius intelligence analyst at a national think tank. He guest starred in four episodes in The Good Wife as the brother of the character Alicia Florrick.
- Dallas also starred in another AMC television series, Rubicon. Dallas played a genius-level analyst in a New York City federal intelligence agency.