BACKGROUND: Caregivers facing mental and social stressors risk negative outcomes. The UNICEF Caring for the Caregiver package is a counselling approach and behaviour change intervention that can be integrated into routine home-visiting by frontline workers, in a demand-responsive way, at a population level. We aimed to evaluate caregiver outcomes and explore intervention experiences in six low-income and middle-income countries. METHODS: Using a non-randomised pragmatic design, we recruited caregivers of children using community-based sampling. Caregivers reported dose exposure and completed pre-post outcome measures of self-efficacy (General Self-Efficacy scale); social support (Multidimensional Scale of Perceived Social Support); depression (Patient Health Questionnaire-9); anxiety (General Anxiety Disorder 7-item scale); and parenting stress (Parenting Stress Index-36). Using pooled data, two-way fixed-effects regressions examined change and variations in outcomes, by dose. Perception data were collected from caregivers and frontline workers. FINDINGS: In Bhutan, Brazil, Serbia, Sierra Leone, Rwanda, and Zambia we trained 198 frontline workers and recruited 822 pregnant and postnatal caregivers receiving home-visiting from them (April, 2021, to July, 2022). At endline (3-6 months post-baseline) we assessed 682 (83%) of 822 caregivers. We observed higher self-efficacy (β=2·63 [95% CI 1·9 to 3·3]) and social support (4·17 [2·9 to 5·4]), and lower depression (-2·23 [-2·7 to -1·7]), anxiety (-1·43 [-1·8 to -1·0]), and parenting stress (-12·35 [-15·0 to -9·7]). Higher dose was associated with greater change across outcomes. The majority of caregivers and frontline workers reported positive intervention experiences. INTERPRETATION: Across settings, the UNICEF Caring for the Caregiver intervention was positively experienced by caregivers and frontline workers and was associated with positive changes in multiple outcomes. It has potential at population level, but evidence in controlled and longitudinal studies is needed. FUNDING: UNICEF and the LEGO Foundation. TRANSLATIONS: For the Dzongkha, Portuguese, Krio, Serbian, Kinyarwanda and Chichewa translations of the abstract see Supplementary Materials section.