Alexandre Marius Henri Blanc (14 September 1874 - 26 August 1924) was a French schoolteacher, socialist and national deputy.

During World War I (July 1914 - November 1918) Blanc remained with the parliamentary minority that gradually took a more traditional position, leading to the split of the socialist party in 1920.

The Confédération générale du travail (CGT, General Confederation of Labor) leaders Alphonse Merrheim, Albert Bourderon and Marie Mayoux were expected to represent France, but were refused the passports they needed to travel.

Three delegates from the socialist party (SFIO, Section Française de l'Internationale Ouvrière) led by Alexandre Blanc were able to attend as deputies with parliamentary immunity.

Even Jean Longuet, the grandson of Karl Marx and nominally head of the pacifist section of the socialist party, said he would continue to vote for war credits.

[9] Shortly before the war ended, in October 1918 Blanc wrote that his group would support the majority if, as promised, they led the party back to the International, and fight them if they did not.

The left and center of the party wanted to declare solidarity with the Russian Revolution, while Renaudel on the right threatened to resign rather than join the Third International.