He moved to Paris in 1920 and continued his studies at the École Nationale Supérieure des Beaux-Arts in the private workshop of Emmanuel Pontremoli and Auguste Perret.

He knew many artists such as Georges Braque, Joan Miró, Pablo Picasso, Alexander Calder, André Derain, Fernand Léger, and Alberto Giacometti.

During the Second World War, Nelson returned to the United States and acted as chairman of the “France for ever” movement, which aimed to spread French culture to Americans.

In 1963, André Malraux appointed him as Director of Atelier Franco-Américain d’Architecture at l’École Nationale Supérieure des Beaux-Arts.

He was buried in the Varengeville-sur-Mer cemetery, near his wife Madd Giannattasio and the painter Georges Braque, his great friend who had joined him in Normandy in 1929 and for whom he had designed the atelier.

In 1934, Nelson designed the surgical building of the hospital of the Suez Canal company in Ismailia, north-east Egypt.

Despite his work's appreciation, it was not carried out in his innovation and the hospital was built using more traditional designs created by the company architect.

After the war, Nelson worked on his magnum opus: the Centre Hospitalier Mémorial France - États-Unis in Saint-Lô, designed and built between 1946 and 1956, with contribution from the United States.

Nelson took part in an experimental construction project of three modern buildings with the help of Charles Tillon (Minister for Reconstruction and Urban Planning in 1947).