 He served in that role under Ambassadors David K. E. Bruce, James Clement Dunn, and C. Douglas Dillon until 1954.On August 17, 1955, Thayer was nominated as the U.S. Minister to Romania.He was commissioned during a recess of the U.S. Senate and recommissioned after confirmation on January 25, 1956, presenting his credentials on November 10, 1955 and serving until December 12, 1957.