On 25 June of the same year, on the removal of Sir William Blackstone to the Common Pleas, he succeeded him as a judge of the King's Bench, in which court Lord Mansfield then held undisputed sway.
Mr. Justice Ashurst's judgments, which are reported in Loffts and Douglas's 'Reports' and Chitty's 'Practice Cases,' are remarkable for their clearness and good sense.
A contemporary writer thus describes his qualities as a judge: 'Sir William Ashurst is a man of liberal education and enlarged notions.
The charge was delivered shortly after the massacres of September in France, and at a time when the name of reform had become odious to a multitude of Englishmen.
Mr. Justice Ashurst, giving expression to the fears of the hour respecting the French Revolution, attacked as 'absurd, nonsensical, and pernicious' the doctrines of its English admirers.
His personal appearance is recorded in the lines attributed to Erskine — Being highly esteemed as a lawyer, Sir William Ashurst was twice one of the commissioners entrusted with the great seal, which he held from 9 April 1783 to 23 December of the same year and from 15 June 1792 to 28 Jan. 1793.