"She left this week," the US embassy in Vilnius told BNS.
McCarthy, who had served as US ambassador to Lithuania since 2013, will be replaced by Anne Hall who will come to Lithuania in late September or early October.
In the meantime, the US embassy in Vilnius is headed by Chargé D'affaires Ad Interim Howard Solomon.
Hall, a career diplomat, has been acting principal deputy assistant secretary in the Bureau of Oceans and International Environmental and Scientific Affairs at the US Department of State since 2014.
Hall served as principal officer and consul general at the US Consulate General in Krakow, Poland, from 2006 to 2009, and as senior Cyprus desk officer in the Bureau of European and Eurasian Affairs, Office of Southern European Affairs from 2003 to 2005.
She served as deputy chief of mission at the US embassy in Vilnius from 2010 to 2013.