Knapp was born in Biłgoraj. His father's name was Antoni and his mother was Julia, née Wnuk.
In 1935 he began studies at the Lwów Polytechnic. After the outbreak of World War II the Soviet Union occupied Lwów, murdered Knapp's father and sent Stefan to a gulag in Siberia. There, among other things, he worked building schools for Russian children who had been orphaned because their parents had been imprisoned or murdered for political reasons.While in the Gulag, because artistic endeavors were limited, he made chess sets out of bread and playing cards out of trash for his fellow prisoners
Knapp was known for producing murals of unprecedented size with materials which were meant to last for thousands of years. He first received wide attention and acclaim during his exhibition in London in 1954. There he presented a unique and innovative style and technique, which involved melting glass into pieces of light steel, using specially made furnaces. Prior to finding fame he worked as a ski instructor in the Swiss Alps to make ends meet
He died in 1996 at his studio in London, still working on his art. Thousands of people attended his funeral in London.Wikipedia