A business leader from the age of 29 (from 1922 to 1940), Weiller developed the most important airplane engine factory in Europe, Gnome et Rhône, which became Snecma S. A. after nationalization in 1945.

In 1940, Weiller and his family, his wife Aliki, his son Paul-Annik and his mother-in-law, Hélène Diplarakos, travelled to Bordeaux, France, where they received transit visas to Portugal from the Portuguese consul Aristides de Sousa Mendes, on 22 June.

He escaped in January 1942, fleeing first to Morocco, then to Cuba, and finally to Canada, where he contributed to the efforts of France libre (he was issued passport no.

He subsequently became a philanthropist of the arts; through his influence and financial support, he contributed to the restoration of the Palace of Versailles, created a ballet company, and aided a number of artists (Robert Hossein, Roger Vadim, Maurice Béjart, Michèle Mercier, Brigitte Bardot, Alain Delon, etc.).

Paul-Louis Weiller led an active social life associating with the royal families of Europe, business and political leaders (Aristotle Onassis, Henry Ford II, Jean Paul Getty, Richard Nixon, and Georges Pompidou, some of whom from time to time worked for him), and personalities in the arts and entertainment, whom he gathered in last of the salon traditions as described by Marcel Proust.

His home on the French Riviera, the villa La Reine Jeanne (designed by the American architect Barry Dierks), attracted international society for the greater part of the 20th century.