In 1940, after losing a race for alderman, he challenged Socialist incumbent Assembly member Arthur Koegel in the seventh Milwaukee County Assembly district (7th ward of the City of Milwaukee); Schreiber won a four-way Republican primary, but Koegel won the general election with 4248 votes, to 3973 for Schreiber and 1828 for Democrat Clarence Findley.[2]
In 1942, he faced Koegel once more and won, with 2696 votes to 1652 for Progressive Walter Ensslin and only 818 for Koegel. He was assigned to the standing committee on State Affairs.[3]
In 1944, Schreiber defeated veteran Socialist Alex C. Ruffing in the spring municipal election for alderman, and did not seek re-election to the Assembly, although he did serve out his term after being sworn in as alderman.[4] He would remain on the Common Council until 1976. His seat in the Assembly was taken by fellow Republican Clyde Follansbee.