 He worked as comptroller and vice president of Brunswick Laundry in Jersey City starting in 1937.He entered the United States Army as a private in 1942, served in the Italian Campaign with the 92nd Infantry Division in 1944 and 1945, was a captain, Military Government Division in Austria, in 1945 and 1946, served with Tenth Corps in Korea in 1950, was discharged to the Infantry Reserve as a major in 1950 and promoted to lieutenant colonel in 1956.Sieminski was elected as a Democrat to the Eighty-second and to the three succeeding Congresses, serving in office from January 3, 1951, to January 3, 1959, and was an unsuccessful candidate for renomination in 1958.