Born in Saint-Amand-les-Eaux, Nord department of France in a family of carillonneurs, Lannoy was quickly introduced to the bell tradition.
He was accepted at the Conservatoire de Paris and obtained the supreme awards in the writing classes.
Sent to Ukraine, in the disciplinary camp of Rawa Ruska, he attempted another escape in 1942, which led to his internment at the citadel of Lemberg.
Then sent to Austria in 1943 in a Stalag, he was appointed Kapellmeister and organized orchestras, choirs and even a ballet-mime, Pygmalion, played by prisoners in Poland.
At the request of the Americans, he composed the music for the documentary film Homecoming, recounting the return of prisoners after the Second World War and directed by Henri Cartier-Bresson.