Former US Ambassador to Bulgaria James Warlick will join Egorov Puginsky Afanasiev & Partners (EPA&P), a Russian law firm, as of January 2017.
Warlick made the announcement on Twitter, thus putting an end to 30 years of service for the US Department of State.
Currently he is the OSCE Minsk Group Co-Chair, a role he will leave on December 31.
An Armenian official said on behalf of the Minsk Group Warlick's term had come to and end and he was substituted as a rotation principle is applied for American co-chairs.
EPA&P is the biggest Russian law firm. Warlick will be on its team in Washington.
He served as Ambassador to Bulgaria between 2010 and 2012.