Background. Older people are one of the groups particularly vulnerable to loneliness due to factors such as deteriorating health, widowhood and death of friends/family, fewer confiding relationships, and being more likely to live alone. In the United Kingdom, services to alleviate and/or prevent loneliness can be classified as foundation services, direct interventions, gateway services, and structural enablers. Service managers and personnel involved in the delivery of interventions for older people are well-positioned to report on the mechanisms that contribute to the effectiveness of interventions. This study aimed to elicit from the perspective of a range of service providers, the barriers and facilitators of successful service provision, and the reduction of loneliness among older people. Methods. Semistructured interviews were conducted with 23 service managers of services providing an intervention to older people in Northern Ireland. Services were eligible for inclusion if they reported a goal of preventing or reducing loneliness and/or social isolation among older people. Transcripts were analysed using thematic analysis. Results. Eight themes were produced representing barriers or facilitators of successful service delivery, including characteristics of the service (person-centred approach, empowerment of service users and staff/volunteers, personal qualities of staff and volunteers, and funding for service provision) and characteristics of the wider community were services were located (hard to identify and/or reach lonely people; education and awareness of services; family and community structures; and accessible, affordable, and safe public transport). Conclusion. Developments in this area should prioritise integrated, systemic solutions that harness capacity and partnership working within communities, grounded in the principles of empowerment, inclusion, self-determination, and collective action.