We explored temporal associations between public greenspace and adults' mental wellbeing. Participants (n = 5,906) aged 40-65 years at baseline had data at >2 post-baseline waves of HABITAT, a multilevel longitudinal study (2007-16) in Brisbane, Australia. Participants self-reported mental wellbeing (short Warwick-Edinburgh Mental Wellbeing Scale) and neighbourhood self-selection reasons at Waves 2-5 (2009-11-13-16). We examined associations between Δgreenspace (within 1 km of home) and Δmental wellbeing using a linear fixed effects model, adjusting for time-varying confounders. Mental wellbeing increased (β = 1.75; 95% Confidence Interval:0.25-3.26) with greenspace exposure, adjusting for self-selection. Urban planning and policy initiatives to increase public greenspace may benefit mental wellbeing.