He was a partner and eventually the head of Culverwell, Brooks, Cotton & Company, leather, hide and tallow brokers, based in the City of London. In 1866 he became alderman for Lime Street Ward on the Corporation of London. In 1868 he was Sheriff of London and Middlesex. He was a member of four livery companies: the Haberdashers, the Saddlers the Turners and the Fan Makers.
At the 1868 general election he was Conservative candidate for the Southwark constituency, but failed to be elected.
When the first London School Board was elected in 1870, Cotton was one of the representatives of the City of London. He served three three-year terms, retiring from the board in 1879.
At the 1874 general election he was returned as one of the City of London's four members of parliament, holding his seat until 1885.
He was Lord Mayor of London in 1875-76. In 1888 he became an alderman for Bridge Within Ward, finally retiring from the Court of Aldermen in 1892. In that year he was knighted and unanimously elected Chamberlain of London.
He died after a long illness at his home in Bramham Gardens, Earl's Court.
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