On 10 April 1824, at St George's, Hanover Square, he married Mary Anne (1797–1891), daughter and coheir of John Mansfield of Birstall.
Turner's father, Richard, was a friend of George Canning, who gave William a post in the Foreign Office.
Byron replied in a letter to John Murray published at the time, and Turner, in a counter rejoinder, overwhelmed his adversary with quotations from ancient and modern topographers.
During the absence of an ambassador, due to the removal of Lord Strangford to Saint Petersburg, Turner filled the office of minister plenipotentiary.
On 22 October 1829 he was appointed Envoy Extraordinary and Minister Plenipotentiary to the Republic of Colombia, and after filling that post for nine years he retired from the service.