The Vatican announced the appointment today.
Archbishop Viganò, 70, succeeds Archbishop Pietro Sambi, who died in July from complications following lung surgery.
Carlo Viganò was ordained a priest in 1968, and has been serving in Vatican diplomacy for almost 40 years.
Since 2009, he had been secretary of the Governorate of Vatican City State.
Archbishop Timothy Dolan, the president of the U.S. episcopal conference, welcomed the nuncio with a letter today, telling him that he would “serve as a continuing sign to us of that source of renewal and hope that Pope Benedict brought to our country.”