Objective: To compare risks of adverse birth outcomes between maternally vaccinated and unvaccinated twin pregnancies. Design: Multi-jurisdictional data linkage cohort study. Setting: We examined all registered births in Queensland (Qld) and Northern Territory (NT), Australia between 1 January 2012 and 31 December 2017. Population: Women carrying a multiple pregnancy ≥20 weeks gestation and weighing ≥400g. Methods: We used Cox proportional-hazard models to calculate risk, with maternal vaccination status as the time-varying exposure, and national birthweight percentile charts specific for Australian-born twins to accurately reflect risk among small for gestational age (SGA) infants. Main Outcome Measures: Adverse birth outcomes including stillbirth, preterm birth and SGA infants. Results: Among our cohort of n=11,945 infants, there was no statistically significant increased risk of preterm births, stillbirths or SGA infants between women who received a maternal influenza and/or pertussis vaccination and unvaccinated women. There was a borderline reduced risk of SGA infants among Qld women who received pertussis vaccination (aHR 0.82, 95% CI 0.68–1.00, p=0.051). Conclusion: We provide evidence that maternal influenza and pertussis vaccinations did not increase the risk of stillbirth, preterm birth or SGA infants among women carrying a multiple pregnancy. These novel and important findings alleviate ongoing safety concerns for a cohort that carries a higher baseline risk of adverse birth outcomes compared to singleton pregnancies. Keywords: maternal vaccination; pertussis; influenza; twins; multiple pregnancy; safety