Career
He was Lord Mayor of London in 1848-1849, and sat in the House of Commons from 1837 to 1865. He was elected as Sheriff of the City of London in 1837 and Lord Mayor of London in 1847. In June that year a vacancy arose in the City of London constituency when the Liberal Member of Parliament James Pattison died age 62.
A group of leading Liberals from the City met on 16 July and resolved to nominate Duke for the vacancy if he would consent, agreeing that:
A deputation was sent to the Mansion House, where Duke was asked to stand, which he immediately agreed to do.
He was made a baronet in October 1849, on 30 November he was appointed as a commissioner for enquiring into Smithfield Market. He held the City of London seat until he stood down from the Commons at the 1865 general election.
He was appointed High Sheriff of Sussex for 1872.