He was best known for his paintings of wars of which he had been an eyewitness.
Montyn was born in a conservative Calvinistic family and was raised in Oudewater.
In the Second World War he joined the German navy and fought on the eastern front.
After the war he lived in France and in the Netherlands.
His work is displayed in the Bibliothèque Nationale in Paris, the Museum of Modern Art in New York and the Museum Boijmans Van Beuningen in Rotterdam. Montyn died on 13 August 2015 in Amsterdam, aged 90.