After attending university in Paris, Longuet worked as a journalist and trained as a lawyer. He worked for the newspaper ''
L'Humanité and was a founder and editor of the newspaper Le Populaire''. He was active in one of France's principal socialist parties, the
French Section of the Workers' International (SFIO), and served both as a mayor and as a member of the French
Chamber of Deputies. During the
First World War, he was a pacifist but also supported war credits. At the Strasbourg Congress in 1918 his policy was adopted by the majority of the socialist SFIO. After the
Tours Congress of 1920 had the
Communists gain the majority, he supported the minority and joined the
centrist Two-and-a-half International, the Vienna Union. He criticised the
League Against Imperialism, which was created in 1927 and supported by the
Comintern. Longuet supported
Zionist positions at the
Socialist International meeting in Brussels in 1930 and at a speech to a Zionist group in Paris in 1935. He also represented
Vinayak Damodar Savarkar, a political prisoner, who while being taken from Bombay to England to stand trial on the charges of sedition and abetment of murder, escaped from the ship, which was docked at
Marseilles, and swam ashore until he was caught by a French
gendarme. The case drew criticism from the French socialist press, which decried that the individual rights of Savarkar had been trampled as a result of his arrest by British constables on French soil, which they believed to violate the sovereignty of France. Pressure from the leftist and liberal press continued and forced both countries in October 1910 to take their case to the
Permanent Court of Arbitration in
The Hague.
Madam Cama, a revolutionary Parsi woman from Bombay who was one of the founders of the Paris Indian Society, managed to get power of attorney, which facilitated the engagement of Longuet as Savarkar's representative in The Hague. However, as the arbitration was between France and Britain, the tribunal did not accept Longuet's memorandum on behalf of Savarkar, considering it out of the terms of reference. However, Longuet persisted and personally handed over the copies of the memorandum to the members of the court. ==Death and family==