The first venture of Mahatma Gandhi in all India Politics was

The correct choice is: “Rowlatt Satyagrah”

Gandhi's early Indian campaigns, Champaran (1917), Ahmedabad mill strike (1918) and Kheda (1918), were local struggles. His first all-India movement was the Satyagraha against the Rowlatt Act in 1919, for which he formed the Satyagraha Sabha and called a nation-wide hartal on 6 April 1919.

The “Champaran Movement” (1917) was his first satyagraha in India, but it was confined to the indigo cultivators of one district of Bihar. The “Non-cooperation Movement” (1920–22) and the “Dandi March” (1930) came later.