In 1848 he was appointed chargé d'affaires of the United States to the Holy See.[3] Martin, a Protestant, was chosen over a few candidates who were openly friendly to Vatican. He reached Rome on August 2, 1848, but hesitated to enter the city owing to continuing revolution.[4] Martin presented his credentials to the Holy See on August 19, 1848, but died seven days later[5] and was buried in the city's Protestant Cemetery.[6]