Jon M. Huntsman Jr., the United States ambassador in Moscow who carried out President Trump’s policies during a highly turbulent period of sanctions and investigations into Russian electoral interference, resigned on Tuesday.

The move had been expected amid reports that Mr. Huntsman, a former Utah governor, would return to politics in his home state.

Mr. Huntsman had kept a low profile through much of his tenure in Moscow, as a special prosecutor in the United States investigated Russian interference in the 2016 election. He had been nominated by Mr. Trump as the new administration took over in 2017.

In his resignation letter, Mr. Huntsman said he was honored by the trust that Mr. Trump had placed in him “during this historically difficult period in bilateral relations.”