twisleton-wykeham-fiennes was born on 22 september 1920, the son of ivo murray twisleton-wykeham-fiennes, 20th baron saye and sele, and hersey cecilia hester butler. despite a family connection with winchester college, he was educated at eton, and then at new college, oxford. during the second world war he served in the rifle brigade (prince consort's own). he received an emergency commission in the rifle brigade on 19 april 1941, and was promoted war-substantive lieutenant on 1 october 1942 and temporary captain on 3 september 1943. in march 1945, he was mentioned in dispatches for service in north-west europe. after the war, fiennes remained in the army, receiving promotion to war-substantive captain and temporary major on 15 january 1946. on 22 may 1948, he received a regular commission as a lieutenant in the rifle brigade (seniority from 22 may 1943), with promotion to captain effective from the same date (seniority from 22 november 1947). he was stationed in palestine during the palestine emergency in 1946-47, for which he was again mentioned in dispatches in january 1949. he resigned his commission on 8 february 1950, leaving with the honorary rank of major.