Kompfner was born in Vienna to Jewish parents. He was originally trained as an architect and after receiving his university degree in 1933 he moved to England (due to the rise of anti-Semitism) where he worked as an architect until 1941. However, he had a strong interest in physics and electronics, and after being briefly detained by the British as an enemy alien at the start of World War II he was recruited to work in a secret microwavevacuum tube research program at the University of Birmingham. While there, Kompfner invented the TWT in 1943. After the war he became a British citizen, continued working for the Admiralty as a scientist, and also studied physics at the University of Oxford, receiving his PhD in 1951.