Having exiled himself to Switzerland to avoid fighting for France in World War I, he left for Ireland, where he established good relations with nationalist leaders.
Le Roux contributed to the journal La Bretagne libertaire in 1921.
In 1922, he translated into French the works of Ramsay MacDonald.
He also wrote one of the earliest biographies of Patrick Pearse.
Eventually, and perhaps surprisingly, he became private secretary to the Conservative politician Harold Macmillan, before being killed during the London Blitz of World War II.