After the close of the war, he continued in the service and was on detached duty at the United States Military Academy, West Point, New York.
Sosnowski rose to the rank of captain and adjutant in the Thirty-first Regiment, Infantry, Michigan Army National Guard, from 1909 to 1916, with service on the Mexican border in 1916.
In 1927, US Representative John B. Sosnowski stated "I would suggest you gentlemen read a book published by Blair Coan, entitled The Red Web," as part of a long list of findings presented during a public congressional hearing.
[1] He was an unsuccessful candidate for re-nomination in 1926, when his 1924 Democratic rival, Robert H. Clancy, switched parties to become a Republican and defeated Sosnowski in the primary.
He resumed the real estate and brokerage business in Detroit and was chosen as a delegate to the Republican National Conventions in 1932, 1936, 1940 (as an alternate), and 1944.