The Capitals announced the deal Friday for the 30-year-old defenseman, who has three goals, four assists and 43 penalty minutes in 31 games this season.
Erskine finished last season with a career-best plus-16 rating, his third straight season with a plus rating. He is plus-3 this season.
Erskine signed with the Capitals as a free agent in September 2006. He has appeared in 354 career NHL games with Dallas, the New York Islanders and Washington, recording 10 goals, 28 assists and 673 penalty minutes.