Cornish was elected Mayor of Washington, New Jersey, in 1884, and reelected in 1885 and 1886. He declined renomination in 1887 and in 1888. He served as member of the
New Jersey Senate from 1891 to 1893, representing
Warren County.
Congress Cornish was elected as a
Democrat to the
Fifty-third Congress, serving in office from March 4, 1893 to March 3, 1895. He was an unsuccessful candidate for reelection in 1894 and lost again in 1896. He accompanied William Jennings Bryan on his whistle stop tour through New Jersey, pausing in Washington on September 23, 1896. ==Later career and death==