He was a member of a junior branch of the Delaval family of Seaton Delaval, Northumberland. He was born at North Dissington, Ponteland, Northumberland which estate he ultimately inherited and sold to Edward Collingwood of Bykker in 1673.
He was promoted to Vice Admiral of the Red in 1692. At the Battle of La Hogue on 9 May 1692, he personally commanded HMS Royal Sovereign and was responsible for the destruction of the French flagship and two others at Cherbourg. His Royal Sovereign log books (1691-1693) are preserved in the archives of the New York Public Library.
In 1693, Delaval, along with Henry Killigrew and Cloudesley Shovell replaced Edward Russell as commander-in-chief. However, in the summer the French isolated and inflicted severe damage on the Smyrna convoy in the Mediterranean at the Battle of Lagos, for which Delaval, Killigrew and Shovell were severely criticised. A censure motion was laid in the House of Commons alleging 'notorious and treacherous mismanagement'. William was forced to dismiss his naval advisor Secretary of State the Earl of Nottingham, and appoint Russell as the new commander-in-chief.
Shortly thereafter, Delaval was involved in intrigue at court where he was regarded as a possible Jacobite sympathiser and he lost his command. He retired to Northumberland. He died in 1707 and was buried in Westminster Abbey.