Jack was born in July 1921 in Leeds to Morris and Margaret neé Zimmerman. The family surname was originally Barofsky and Morris changed it to Brown when he served in the Army in WW1. Margaret was born in Leeds to Augustus Zimmerman who was born in Germany. Margaret died when Jack was three and he was raised by his widowed father and his Aunt Rebecca (Beatie).

Jack was the wireless operator of Wellington X3713 which took off from RAF Honington on a night operation to Emden. The aircraft was shot down by a night-fighter Oblt Egmont Prinz zur Lippe Weissenfeld 11. and crashed NW of Groningen, Holland. The crew were:
Observer, F/Sgt Arthur Dunham Adair, RCAF  
W/Op A/G, P/O John David Baxter W/Op A/G, P/O Alfred Victor Brooks Sgt Jack Brown  
Pilot, Wing Commander Leslie Vidal James