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Amines—organic molecules carrying the –NH _2 moiety—have been recognized as a vital intermediate in the formation of prebiotic molecules such as amino acids and nucleobases. Here we report the formation of vinylamine (C _2 H _3 NH _2 ), which was recently detected toward G+0.693–0.027, in interstellar ice analogs composed of acetylene (C _2 H _2 ) and ammonia (NH _3 ) exposed to energetic electrons. Our experiments mimic cascades of secondary electrons in the tracks of galactic cosmic rays impinging on interstellar ice in molecular clouds. Tunable photoionization reflectron time-of-flight mass spectrometry (PI–Re-TOF–MS), along with isomer-specific assignments, reveals the production of vinylamine (C _2 H _3 NH _2 ). Quantum chemical computations suggest that both a radical–radical recombination of the amino (NH _2 ) with the vinyl (C _2 H _3 ) radical and a one-step concerted route are feasible pathways to vinylamine (C _2 H _3 NH _2 ). The results present the first documented route to form vinylamine in interstellar ice analogs. This unsaturated amine, which is isovalent to vinylalcohol (C _2 H _3 OH), could be a key precursor for the abiotic synthesis of prebiotic molecules such as amino acids and nucleobases, with implications for the origins-of-life theme.