Dancy will play the recurring role of John Zabel, "a savvy Washington consultant who joins the White House as a new foreign-policy adviser to the president and a formidable opponent to Saul Berenson (Mandy Patinkin,)" a news release said.
The eighth and final season of the show is in production. It is expected to premiere later this year.
Beau Bridges will play the U.S. president this season, while Sam Trammell will play the vice president.
Danes returns in the central role of Carrie Mathison, a former CIA operative with bipolar disorder who recently spent months in confinement in a Russian gulag.
"Her body is healing, but her memory remains fractured -- which is a problem for Saul, now National Security Adviser to the newly ascendant President Warner," a synopsis said. "The top priority of Warner's young administration is an end to the 'forever war' in Afghanistan, and Saul has been dispatched to engage the Taliban in peace negotiations."
The cable network announced in August that Season 8 would be the show's last.
Danes gave birth to her second son with Dancy in September. Married since 2009, they are also the parents of 6-year-old.