The article is dedicated to the 100th anniversary of the adoption of the first Russian constitution in 1918. Despite the diversity of opinions on constitutionalism in Russia, the article pays attention to the relationship between the constitutional process in the history of Russia. The Soviet Constitution of the RSFSR of 1918 is analysed in the context of radical transformations in Russia in the first decades of the 20th century, determined by the transition from monarchy to the republic during the February and October revolutions of 1917. The author justifies the idea that the period after the seizure of power by the Bolsheviks in October 1917 before the dissolution of the Constituent Assembly in January 1918, it was accompanied by attempts to preserve the traditional legal legitimacy for justifying the legitimacy of the seized power. The Constituent Assembly fixed that historical situation of “nonlaw” when the rule of law without power proved incapable of establishing a legal order. The primacy of politics in relation to law, implemented by the Bolsheviks, led to the transition from legitimate revolutionarism to the establishment of the so-called revolutionary legality, expressed in the Constitution of 1918. The main directions of discussions in the process of forming a constitutional project - the dictatorship of the proletariat and democracy, the national and territorial principles of construction of federation, the relationship between the legislative and representative authorities, as well as the structure and basic principles of the adopted basic law. The mobilisation character of the constitutionalism of this period was also determined by the policy of military communism, or “the direct construction of communism” by military-political methods. The historically conditioned character of the Soviet constitutionalism, dependent on the struggle for power and the political strategy of development is substantiated.