INTRODUCTION: Sleep disturbances are common and distressing for people with dementia and their family caregivers, with limited treatment options. The DREAMS START (Dementia RElAted Manual for Sleep; STrAtegies for RelaTives) multi-component intervention for sleep disturbance in people at home with dementia is clinically and cost-effective at 8 months. In this long-term follow-on study, we assessed 2-year clinical effectiveness. METHODS: We recruited dyads of people with dementia and their family caregivers from community settings, for a two-arm, multi-center, single-blind, parallel-arm, superiority trial with the primary outcome Sleep Disorders Inventory (SDI). Analyses were intention to treat. RESULTS: We randomized 377 dyads, 189 to treatment-as-usual (TAU) and 188 to intervention; 177 dyads (46.9%) were followed up at 24 months. Two-year adjusted mean SDI score was lower in the intervention arm than TAU (-5.40; 95% CI -9.14 to -1·67; p = 0·005). DISCUSSION: In this follow-on study we demonstrate 2-year improvement in sleep disruption for people with dementia. DREAMS START has potential for delivery at scale.