Marine species raft on floating litter, including various plastics, potentially spreading non-native species and threatening global marine habitats. Despite limited attention, Didemnum vexillum, an invasive colonial tunicate in Europe, colonized coasts of southwest Scotland (2009) and northeast Ireland (2012), likely transported via rafting. We studied D. vexillum survival and performance on three plastic types—HDPE, PS, and PP—finding high survival rates over 42 days, with colonies thriving best on PS. Using these data, hydrodynamic and particle tracking models simulated dispersal from existing Irish Sea colonies, projecting potential rafting distances of up to ~150 km for surface particles influenced by tide and wind, and half that for neutrally-buoyant mid-depth particles driven by currents. Hence, the modelling supports the potential for dispersion of this species within the Irish Sea via rafting. This study highlights marine plastics as a vector that may facilitate widespread dispersal of non-native species.