A five-time Olympic gold medalist, with a total of nine Olympic medals, Sheridan was called "one of the greatest figures that ever represented this country in international sport, as well as being one of the most popular who ever attained the championship honor." He won the discus throw event at the 1904, 1906, and 1908 Summer Olympics as well as the shot put at the 1906 Olympics and the Greek discus in 1908. At the 1906 Intercalated Games in Athens he also won silver medals in the standing high jump, standing long jump and the stone throw.
In 1907, Sheridan won the National Amateur Athletic Union discus championship and the Canadian championship, and in 1908 he won the Metropolitan, National and Canadian championships as well as two gold medals in the discus throw and bronze in the standing long jump at the 1908 Olympic Games.
It is often claimed that Sheridan fueled a controversy in London in 1908, when flagbearer Ralph Rose refused to dip the flag to King Edward VII. Sheridan is supposed to have supported Rose by explaining "This flag dips to no earthly king," and it is claimed that his statement exemplified both Irish and American defiance of the British monarchy. However, careful research has shown that this was first reported in 1952. Sheridan himself made no mention of it in his published reports on the Games and neither did his obituary.
The inscription on the granite Celtic Cross monument marking Martin Sheridan's grave in Calvary Cemetery, Queens, New York says in part: "Devoted to the Institutions of his Country, and the Ideals and Aspirations of his Race. Athlete. Patriot."