Groesbeck's entrance into state politics came in 1912, when he led efforts to select a delegation to the Republican National Convention favorable to the renomination of President William Howard Taft. Groesbeck also actively led the party faction supporting Taft in the general election. In the same year, Groesbeck was elected the state party chairman, serving until 1914. He was a candidate for governor of Michigan in 1914, but lost in the Republican primary election to Chase S. Osborn. In 1916, Groesbeck was elected attorney general of Michigan, and was re-elected in 1918.