BACKGROUND: The impacts of COVID-19 are unprecedented globally. The pandemic is reversing decades of progress in maternal, newborn, child health and nutrition (MNCHN), especially fragile and conflict-affected settings (FCAS) whose populations were already facing challenges in accessing basic health and nutrition services. This study aimed to investigate the collateral impact of COVID-19 on funding, services and MNCHN outcomes in FCAS, as well as adaptations used in the field to continue activities. METHODS: A scoping review of peer-reviewed and grey literature published between 1st March 2020-31st January 2021 was conducted. We analysed 103 publications using a narrative synthesis approach. 39 remote semi-structured key informant interviews with humanitarian actors and donor staff within 12 FCAS were conducted between October 2020 and February 2021. Thematic analysis was undertaken independently by two researchers on interview transcripts and supporting documents provided by key informants, and triangulated with literature review findings. RESULTS: Funding for MNCHN has been reduced or suspended with increase in cost of continuing the same activities, and diversion of MNCHN funding to COVID-19 activities. Disruption in supply and demand of interventions was reported across different settings which, despite data evidence still being missing, points towards likely increased maternal and child morbidity and mortality. Some positive adaptations including use of technology and decentralisation of services have been reported, however overall adaptation strategies have been insufficient to equitably meet additional challenges posed by the pandemic, and have not been evaluated for their effectiveness. CONCLUSIONS: COVID-19 is further exacerbating negative women's and children's health outcomes in FCAS. Increased funding is urgently required to re-establish MNCHN activities which have been deprioritised or halted. Improved planning to sustain routine health services and enable surge planning for emergencies with focus on the community/service users throughout adaptations is vital for improved MNCHN outcomes in FCAS.