Affected by the horrors of World War I, Lagrange reserved in particular his services to victims of tuberculosis, of lung diseases and of poison gas.
Lagrange became a writer with the newspaper Le Populaire, the press organ of the SFIO, and held there a chronique on legal topics.
Following the victory of the Popular Front at the 1936 legislative elections, Lagrange was then named under-secretary of State for Sport and given responsibility for the organisation of Leisure, under the authority of the Minister for Public Health Henri Sellier.
It was the first time that France had such a state secretary, and the Popular Front enacted the first paid holidays (2 weeks), among other social reforms.
Lagrange strongly opposed the fascist model of sport, which transformed it into a substitute for belligerent activities and instrumentalized it in a militarist manner.
Lagrange was at the origin of the creation of the popular leisure pass which grants 40% of reduction on rail-bound transports, while he encouraged and impelled the movement of youth hostels.
Lagrange chaired these days in person, along with Minister of Transport Pierre Cot, André Malraux, who later fought in the International Brigades, and other figures of the Popular Front.
A communist deputy declared: "Going to Berlin, is making oneself am accomplice of the torturers...." Nevertheless, on 9 July, when the whole of the French right voted “for” the participation of France in the Olympic Games of Berlin, whilst the left (French Communist Party included) abstained itself — with the particularly notable exception of Pierre Mendès France, who would become Prime Minister under the Fourth Republic and negotiate the peace agreements with the Viet-minh in Indochina in 1954.
Nevertheless, several French sportsmen decided to boycott the Berlin Olympic Games anyway, and go to Barcelona where the People's Olympiads were scheduled to begin on 19 July 1936.