Sir William Pritchard or Prichard (1632?–1705) was an English merchant and politician, Lord Mayor of London in 1682.
Born about 1632, was the second son of Francis Prichard of Southwark, and his wife, Mary Eggleston. He is described as merchant taylor and alderman of Broad Street.
In 1672 Prichard was Sheriff of London, and he was knighted on 23 October in that year. On 29 September 1682 he went to the poll as court candidate for the mayoralty, and on 4 October the recorder declared him third on the list, below Sir Thomas Gold and Alderman Henry Cornish, both Whigs. But a scrutiny of the poll gave him the first place. On the 25th he was declared elected by the court of aldermen, and on the 28th was sworn in at the Guildhall Prichard's election was celebrated as a great triumph for the court party, in loyal ballads and congratulatory poems. One of these "new loyal songs and catches" was set to music by Henry Purcell.
In office as mayor, Prichard carried on the policy of his predecessor, John Moore (Lord Mayor). He refused to admit to their offices the recently elected whig sheriffs, Thomas Papillon and John Dubois, whose election he had assisted Moore in setting aside. When, in February 1684, proceedings were taken against him by the Whigs, he refused to appear or give bail, and on 24 April was arrested by the sheriff's officers at Grocers' Hall; he was detained in custody for six hours. The arrest caused a furore and the corporation was forced to disclaim any part in it by an order in common council on 22 May. Prichard retaliated by an action for false and malicious arrest against Papillon (Dubois being now dead). The case was tried before George Jeffreys at the Guildhall on 6 November 1684, the law-officers of the crown appearing for the plaintiff, and Serjeant John Maynard for the defendant. Jeffreys summed up strongly in favour of Prichard, who was awarded £10,000. damages. Papillon fled the country to escape payment. Prichard declared his willingness to release him from the effects of the judgment, with the king's assent; this was long refused by James II, but was ultimately granted in 1688, when, on 7 August, Sir William gave a full release to Papillon at Garraway's coffee-house, drinking his former foe's health .