William Duncan was a grocer, general merchant and Lerwick Town Councillor. Duncan had many sporadic stints in the council, first from 1874 to 1876, then when the council had a vacancy to fill in 1880 he was a councillor until 1884. Again, the council turned to Duncan due to a vacancy after the 1884 election, and he then served until he tendered his resignation on July 12th (which was finally accepted by the council on October 15th). He unsuccessfully contested the 1876 Lerwick Town Council election and the 1884 election.
