He moved to Chicago, Illinois in 1836 and continued the practice of his profession. He served as city attorney 1837-1839. He served as a member of the Illinois Senate from 1844 to 1860. He served as delegate to the 1860 Republican National Convention. He was appointed Minister Plenipotentiary to the Kingdom of Prussia by President Abraham Lincoln on March 6, 1861, and served until 1865.
Judd was elected as a Republican to the Fortieth and Forty-first Congresses (March 4, 1867-March 3, 1871). He declined to be a candidate for reelection in 1870. He was appointed collector at the port of Chicago by President Ulysses S. Grant on December 5, 1872, and served until his death in Chicago at age 63.