After leaving the University of Pennsylvania in 1881, Thayer entered the service of the
Pennsylvania Railroad as a clerk in the Empire Line office, remaining in that position for about eighteen months, when he was transferred to the general freight department. After holding various positions in 1888 he was appointed freight solicitor of the
United Railroads of New Jersey division. From February, 1889, to May, 1892, Thayer was out of railway work before returning to the PRR in May, 1892, as division freight agent of the Northern Central, with headquarters at Baltimore, MD. On December 1, 1894, he was promoted to assistant general freight agent, with office at Philadelphia, Pa., and in March, 1897, was made general freight agent in charge of through traffic. In May 1899, he was appointed general freight agent also of the Northern Central, the Philadelphia, Wilmington & Baltimore, and the West Jersey & Seashore. Thayer was elected fifth vice-president of the Pennsylvania Railroad June 1, 1903, becoming manager of traffic on that road. In October, 1905, Thayer was promoted to fourth vice-president; in March, 1909, third vice-president; and, in March, 1911, second-vice president, his ultimate rank at the company. At the time of his death Mr. Thayer was a senior director of the Pennsylvania Railroad, managing the railroad's busiest operations east of Pittsburgh, including those of the Long Island and the New York Connecting roads. Thayer was also director and president of the Erie & Western Transport Union Company as well as a director on the Norfolk & Western and the Leigh & Hudson River roads. He was a member of a large number of prestigious clubs and organizations, including the Philadelphia Club, the Union League and the Union Club of New York, the Metropolitan Club of Washington. D. C, the Railroad Club of New York, and the Chamber of Commerce of the State of New York. A minute adopted by the Board of Directors of the Pennsylvania Railroad after his death said in part: ==The
Titanic==