He served as Mayor of Plainfield, New Jersey from 1912 to 1913. He was chairman of the Union County Democratic committee in 1914 and of the Washington Rock Park Commission of New Jersey from 1915-1921. Stewart served as a member of the New Jersey State Board of Education from 1919–1921 and of the New Jersey State Highway Commission from 1923-1929. He was a delegate to the Democratic National Conventions in 1920 and 1928.