Steiwer started his career in public office in 1909 as the deputy district attorney for Umatilla County, serving until 1910. In 1912, he was elected as the district attorney for the county and served until 1916. That year he was elected to the state senate as a Republican representing Umatilla County and District 20. Steiwer only served during the 1917 legislative session, resigning to enlist in the U.S. Army during the First World War. He served from 1917 to 1919 in the Sixty-fifth Field Artillery with rank of first lieutenant.