Abstract 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.