Cavanaugh was born on July 4, 1823, in
Springfield, Massachusetts. Educated at local schools, he worked for newspapers. He later studied law, and was admitted to the bar in 1854, beginning his practice in
Davenport, Iowa. In 1854 or spring 1856, he moved to
Chatfield, Minnesota, and continued the practice of law. In 1856, he was chosen to manage a land grant in Chatfield. A Democrat, Cavanaugh and
William Wallace Phelps were elected to the
United States House of Representatives from its
at-large district, as part of the first legislature following Minnesota's admittance as a state. On May 28, 1868, he stated within the House of Representatives "I like an Indian better dead than living. I have never in my life seen a good Indian – and I have seen thousands – except when I have seen a dead Indian"; similar statements were also ascribed to
American Indian Wars officer
Philip Sheridan, which he denied making. Cavanaugh was known for his speaking ability. He served from May 11, 1858, to March 3, 1859. He lost his re-election in 1858. In 1861, Cavanaugh moved to the
Colorado Territory, and continued practicing law, as well as mining. He was a member of the Colorado Constitutional Convention of 1865. In 1865, he moved to the
Montana Territory, again serving in the House of Representatives, from its
at-large district. He served from March 4, 1867, to March 3, 1871, having lost his re-election in 1870. He later moved to
New York City and practiced law, returning to Colorado in 1879. He settled in
Leadville, where he died on October 30, 1879. He was buried in
Green-Wood Cemetery, in Brooklyn. ==Notes==