This article explores the political trajectories of the early twentieth-century Grand Duchy of Finland and the Kingdom of Poland in the context of the “global parliamentary moment,” when the constitutional script of revolution competed with the more daring script of social revolution. We scrutinize contrastive political choices of socialist parties in these two western borderlands of the Russian Empire. Finland and Poland emerged as independent parliamentary states in 1917–1918 but under manifestly different circumstances. The Finnish socialist party had enjoyed a stable foothold in the formally democratic but practically impotent national parliament since 1907, whereas the Polish socialists boycotted the Russian Duma and envisioned a democratic legislature as a guaranty of a Poland with true people’s power. The Finnish socialists later abandoned parliamentarism in favor of an armed revolution, in 1918, whereas most of their Polish counterparts used the parliamentary ideal of popular sovereignty to restrain the revolutionary upsurge. We argue that the socialist understandings of parliamentarism and revolution were of crucial importance at this juncture. We draw from a broad corpora of political press reports, handwritten newspapers, and leaflets to show how the diachronic sequence of events and synchronic power relations inside the Russian Empire made certain stances toward parliamentarism and revolution more likely at different points in time.