Grut's first choice would have been to study medicine, and he had gained a place at Pembroke College, Cambridge, but that dream ended with the stock market crash.

In 1936 Grut formed part of the Swedish swimming team at the Berlin Olympic Games, where he saw the German pentathlete Gotthard Handrick win gold in Modern Pentathlon.

Until then, Modern Pentathlon gold medals had been the preserve of Swedish pentathletes: Liliehöök in 1912 (Stockholm), Dyrssen in 1920 (Antwerp), Lindman in 1924 (Paris), Thofelt in 1928 (Amsterdam), Oxenstierna in 1932 (Los Angeles).

Grut had an element of luck in drawing a good horse, Clarian Boy, for the riding event, and from then he went on to complete his best competition result ever.

[1][3] Grut stopped competing after the London Olympic Games and started managing the Swedish Modern Pentathlon team instead.

In 1960, Grut was elected secretary general of the International Modern Pentathlon and Biathlon Union (UIPMB), a post he held for 24 years.