Van Eck was arrested in March 1944 by the Germans at home, in Mol, for his participation in the armed resistance and his assistance to British, Canadian and American pilots who were shot down. He ended up in Dachau together with some friends and his fiancée Mijette Dumalin in Ravensbrück. After much humiliation, torture, hunger and disease, more than once he was near complete exhaustion and faced death. Thanks to the help of friends, good luck and his fighting spirit for survival, he kept on recovering.

After the war, he received the highest American award, the Medal of Freedom, with a certificate from General Eisenhower. He also received an award from the British Airchief Marshall Tedder. His willpower and urge to talk about the terrible crimes committed by the Nazi regime prompted him to write and publish about the camps after the war.

After the war, he revisited all concentration camps and wrote his life's work 'Het boek der kampen' (first edition 1969), which had 11 editions and also a French edition. The work is generally regarded as a standard work on the concentration camps. Son Sis van Eeckhout, who visited all the camps in Europe with his father, revised the book, which was reissued with many new (color) photos in 2015. Ludo Van Eck also wrote a separate book in the form of a novel about many of these camps. He has described a total of fourteen concentration camp novels, some of which were translated into Russian and Bulgarian.