Selwyn was born in October 1922 in Hackney, London to Henry and Polish born Fanny nee Libeskind and he had an older brother Leonard. Further details on the family are unknown to date.

Selwyn enlisted at the end of 1941. He was assigned to 95 Squadron who were based at Bathurst (Banjul) in The Gambia, about 700 miles south of Port Étienne (Nouadhibou) in Mauritania. The squadron had set up an operation base at Port Étienne working in co-operation with the French to launch attacks on U-Boats and to escort troopships and convoys in the Atlantic. 

Selwyn was a controller who was acting as a wireless operator/air gunner on Sunderland DW105. 

Shortly after take-off at 11.05 hours the aircraft was seen returning to base with smoke emitting from it and losing height. The starboard inner engine had developed a fault and caught fire filling the cabin with smoke and fumes making it impossible for the pilot to see. The aircraft failed to make a landing, exploding, and crashing into the water just south of Cansado Point at 11.15 hours. 

2nd Pilot, L. K. J. Spinney survived.

Nav, Kenneth Gilbert Mullett, 139714, killed 
W/Op, A/G, Derek Anthony Roper, 142478, killed 
Pilot Officer Thomas Willoughby Sadleir, 171950, killed 
A/G, Thomas William Ewen, 10046464, killed 
A/G, Gilbert Cameron Gibson, 1369021, killed 
Sergeant David Mason Campbell, 1343817, killed 
Sergeant Charles Ernest Norris, 1280880, killed 
Mechanic, Corporal Roy Stuart Crate, 753247, killed