John H. Baldwin was admitted to the Indiana bar in 1876, at age twenty-five. After practicing law in Indiana for six years, he moved to South Dakota, where he practiced for eighteen years. In 1900, at the age of forty-nine, he and his family relocated again, this time to Frazee, a village in Becker County, where he resumed his law practice. He became local counsel for the Northern Pacific Railroad and was active in community affairs and the Republican Party.
In 1914 he was elected to the state senate representing Becker and Hubbard Counties. He ran without party designation as this was Minnesota's first nonpartisan election. During the 40th Legislature, convened in January 1917, he sponsored and pushed through the legislature a bill that replaced the three member Highway Commission with a single "Commissioner of Highways," who was appointed by the governor. Thereafter he was known as the author of the "one-man highway commission bill." With this triumph he was easily re-elected in 1918 to another four year term. In 1922 he was defeated. He died on June 19, 1924, at age seventy-three.