OBJECTIVE: This case study examines the enabling factors, strengths, challenges and lessons learnt from Timor-Leste (TLS) as it sought to maintain quality essential health services (EHS) during the COVID-19 pandemic. DESIGN: A qualitative case study triangulated information from 22 documents, 44 key informant interviews and 6 focus group discussions. The framework method was used to thematically examine the factors impacting quality EHS in TLS. SETTING: National, municipal, facility levels in Baucau, Dili and Ermera municipalities in TLS. RESULTS: Based on the TLS National Health Statistics Reports, a reduction in outpatient, emergency department and primary care service delivery visits was observed in 2020 when compared with 2019. However, in contrast, maternal child health services simultaneously improved in the areas of skilled birth attendants, prenatal coverage and vitamin A distribution, for example. From the thematic analysis, five themes emerged as contributing to or impeding the maintenance of quality EHS including (1) high-level strategy for maintaining quality EHS, (2) measurement for quality and factors affecting service utilisation, (3) challenges in implementation of quality activities across the three levels of the health system, (4) the impact of quality improvement leadership in health facilities during COVID-19 and (5) learning systems for maintaining quality EHS now and for the future. CONCLUSION: The maintenance of quality EHS is critical to mitigate adverse health effects from the COVID-19 pandemic. When quality health services are delivered prior to and maintained during public health emergencies, they build trust within the health system and promote healthcare-seeking behaviour. Planning for quality as part of emergency preparedness can facilitate a high standard of care by ensuring health services continue to provide a safe environment, reduce harm, improve clinical care and engage patients, facilities and communities.