A Brief History of the Marque
Mercier, Saint Etienne
The André Leducq was manufactured at the Mercier factory in Saint Etienne, which also made Lapébie, Antonin Magne and Louison Bobet, all named for renowned cyclists.
Two models are known, both with Ydral engines - one an L45 four-speed 125cc twin-port two-stroke, and a second with an AJ55 175cc engine and equipped with two large side fairings. Club Ydral has an image of what may be a third model of which only 16 were produced, and another French site lists a 49cc model but without documentation.
André Leducq was famous a cyclist nicknamed "the Joyful Dede", or "Dede of Love and Steel Muscles" (poor translation). He was by far the most popular French rider of the inter-war period and his fame continued long after the war. He participated in nine Tours of France, winning two, 1930 and 1932; he won 25 stages. After racing in the Alcyon team in the 1950s, he was employed by the Mercier company and represented the cycles and motorcycles that bear his name.
He was born on February 27, 1904. After a stint in journalism, André Leducq died in Marseilles on June 18, 1980, as a result of a scuba diving accident. He was 76 years old.
Elsewhere it has been suggested that these were built by Manufrance. They are a Mercier product.
Sources: Club Ydral, Pierre Astier and Wikipedia.