Born to John and Emma Pryor (née Giles) at St Cleer, Cornwall, on 20 March 1874, William John Pryor is first recorded in the Royal Navy as a Boy Seaman 2^nd Class under training in HMS BOSCAWEN (probably at Portland). Records show that he was under training as a Boy 2^nd and, subsequently, 1^st Class at 15 to 16 years old. He went on to sign up to serve in the Navy for a further 12 years of service on 20 March 1892, his eighteenth birthday when he was rated Ordinary Seaman (ORD).

Pryor continued to serve in surface ships as far abroad as South Africa and the Mediterranean, possibly as far east as Egypt in various ships of the Mediterranean Fleet. By this time, the Royal Navy was changing from sail to steam power, and ships were increasingly requiring sailors to have technical as well as seamanship knowledge. During this time William Pryor progressed through Able Seaman (19 December 1893) to Leading Seaman (5 December 1897). Later, while serving in HMS ROYAL SOVEREIGN, he was rated Petty Officer 2^nd Class on 1 October 1899 and PO 1^st Class on 14 March 1901.

Professionally, between 1899 and 1903, he trained to become a submariner, whilst continuing in the Portsmouth area.

Petty Officer 1^st Class William John Pryor joined HMS A5 in 1903 before she was completed on 11 February 1905 and commissioned. He was a member of the crew when A5 and her tender, HMS HAZARD, sailed to Queenstown, (now Cobh) in the Republic of Ireland. On 16 February 1905, whilst berthed alongside HMS HAZARD, an explosion occurred onboard, believed to have been caused by a spark igniting petrol fumes.  He succumbed to his injuries in Haulbowline Military Hospital.

William Pryor and five other members of the crew were killed by these explosions.  He was buried in Old Church Cemetery near Cobh, with full military honours.