Jansen did not seek political office for himself, but in 1880 his neighbors elected him justice of the peace. Later he served as Nebraska state representative and then state senator. He turned down nomination for Governor of Nebraska because of the position's requirement to enforce the death penalty. In 1900 President McKinley appointed Jansen as one of twelve commissioners to the Paris World's Fair. In 1901 he represented Nebraska at the state funeral of McKinley.