Community-based organisations (CBOs) play a critical role in implementing HIV programmes, many of which have historically relied on United States (U.S) donor funding. Recent U.S funding cuts have disrupted community-based HIV programmes, underscoring the need to understand implementers’ experiences to support sustainable service delivery. This study explored how funding instability affected community-based HIV programmes in rural KwaZulu-Natal, South Africa. A qualitative, exploratory design was employed using interviews and focus group discussions with purposively selected youth frontline workers and programme managers (n = 26). The Health Systems Building Blocks framework guided thematic analysis. Participants described disruptions in outreach and prevention services, contract terminations and reduced working hours among frontline personnel, weakened data and follow-up systems, shortages or reduced local availability of HIV prevention commodities, lack of transition planning, and abrupt program closure without sustainability measures. Community-based HIV programmes are a critical component of the local health system, and funding-related disruptions may weaken progress across the HIV care cascade by undermining testing, linkage to treatment, retention, and viral suppression. Protecting these community-based functions is therefore essential for sustaining progress toward epidemic control, while future research should examine the longer-term effects of donor funding reductions on service continuity and health outcomes.