Opting not to return to France during the Russian Civil War, Sadoul co-founded the French Communist Group in Russia, fighting for control of it against Pierre Pascal and Henri Guilbeaux.

[2] A provincial lawyer assigned to the appellate court of Poitiers,[5] and a reserve officer,[6] Sadoul married Yvonne Mezzara (born 1889), who was distantly related to the historian Ernest Renan.

[13] Thomas obtained that Sadoul be assigned to General Henri Niessel's French Military Mission in Petrograd, where he arrived in late September 1917,[2][14] leaving behind his wife and son.

[15] What Thomas hoped to obtain from Sadoul was a direct line of communication between the SFIO and the various socialist groups which either supported or opposed the Russian Provisional Government, and thus to keep Russia on the Entente side.

[18] For the next year, Sadoul was to keep a political diary, described by historian Adam Ulam as "elegantly composed in the form of letters addressed to his French protector and fellow Socialist, Albert Thomas.

[28] In February 1918, as the German Army began its punitive advance on Petrograd, Sadoul offered his expertise as a military saboteur to the Chairman of the Commissars, Vladimir Lenin.

As noted by Lenin, Sadoul also brought with him French monarchist officers, including Guy Louis Jean de Lubersac, who agreed to fight under a communist banner "to secure the defeat of Germany".

[36] In his letters to Thomas, Sadoul also argued that the Bolshevik regime hoped to undo Brest-Litovsk, and therefore cheered for the Anglo–American–French forces during the German spring offensive on the Western Front.

[37] Decades later, he noted that "despite their [...] caste hatred for the [Bolshevik] regime of the masses, most of these officers [assigned to help Trotsky] still understood the material usefulness [...] of partaking in the construction of a new Russian army, one sooner or later capable of resuming the fight against Germany, as an Entente ally.

"[19] Scholar Jean Delmas notes that the Bolshevik pledge to the Entente "rested solely on the personality of Trotsky": "even Sadoul acknowledged that Lenin wrote off any military adventure.

[23] He befriended their spokesman, Alexander Gay, who told him that Bolshevism was being infected by "impure and dangerous elements", and, Sadoul claims, plotted his very own anarchist revolt.

[46] Like the American Oliver M. Sayler, Sadoul was one of the first foreign observers to compare the Bolshevik and French Revolutions, justifying the decimation of Whites, Socialist Revolutionaries, and other "puppets of the Entente", as a political expediency against counterrevolution.

The revolutionary Victor Serge, who spent time attending the Communist Group's sessions, Pascal was more inclined to support the anarchists and Kollontai's "Workers' Opposition".

[65] In late 1918, a French expeditionary corps commanded by Louis Franchet d'Espèrey entered Ukraine and attempted to contain Bolshevik penetration (see Southern Russia intervention).

The Russian government dispatched Sadoul, by then an officer in the Red Army,[8][31][56][66] on a mission to spread anti-war and mutinous propaganda (including Vive la République des Soviets!)

Welcoming the Asian delegates at a public rally on December 5, he voiced his hope for a socialist revolution in France, and suggested that the Communist Group take over representation of French interests in Moscow.

[57] In March 1919, Sadoul was a co-founder of the Comintern, representing a still-to-be-born French Communist Party (PCF) at the International's first-ever meeting,[68] and forfeiting his SFIO mandate.

[2][69] In July, Christian Rakovsky, head of the Ukrainian Council of People's Commissars, assigned Sadoul to negotiate an exchange of prisoners with the French Navy at Odessa.

[78] He was tried in absentia for assisting the enemy and acts of sedition, in what the New-York Tribune described as "a precedent for the attitude of Allied and associated powers toward other nationals who have aided the Bolsheviki [sic].

[82] As noted by historian Nicolas Texier, "the will of certain socialist to maintain the unity of the left" by granting eligible positions to Sadoul and other Bolsheviks cemented in France the notion of a "Red Peril".

[85] The news was welcomed in Europe's right-wing circles: the Romanian D. Nanu noted the socialists' "brazenness" in putting up "the traitor Sadoul"; the results, he argued, showed that "the fatherland ideal" prevailed over the Comintern.

[89] He also played a part in organizing the Congress of the Peoples of the East, but criticized Comintern Secretary Karl Radek for allowing the delegations to include anti-colonial nationalists rather than just communists.

[90] However, he played a part in expelling from Russia the SFIO's Ernest Lafont—he accused Lafont of not wanting to divulge information he had received about the Polish maneuvers in the Battle of Warsaw.

[102] During that interval, the White émigré paper Dni alleged that Sadoul had squandered the 1.4 million chervontsev that the Comintern had provided for stirring up revolt in the French colonial empire.

[105] The PCF intended to present Sadoul and Guilbeaux as its main candidates in the May 1924 elections, but the authorities censured this move; the communist list was consequently changed to include Hadjali Abdelkader, an Algerian independence militant.

[8] During the mid 1930s, Sadoul served as a direct link between the Soviet diplomats and Pierre Laval, the French Prime Minister and signer of the Franco-Soviet Treaty of Mutual Assistance.

[140] Following the February 1934 riots, siding with Doriot and Eugen Fried, he endorsed the creation of a Popular Front—this barrage of anti-fascist parties was disliked by Thorez, who still centered his discourse on criticism of the SFIO.

[147] Historian Stéphane Courtois argues that, with Sadoul's help, Stalin sought to downplay his Nazi alliance as a "reversible strategy", and therefore to alleviate the fears of Herriot and Daladier.

In this capacity, he confiscated the Villa Massilia, owned by a collaborationist, and assigned it to the Union of Jews for Resistance and Mutual Aid, which turned it into a haven for the orphans of the Holocaust.

[8] Their direct descendants include great-grandson Eric Lemonnier, a Paris psychiatrist specializing in autism; Lemmonier's mother was a politician of the conservative Rally for the Republic in the 13th arrondissement, and his father a producer for France 3.