Globally, despite the decline in under-five mortality rate from 213 per 1000 live births in 1990 to 132 per 1000 live births in 2018, the pace of decline has been slow, and this can be attributed to poor progress in child survival interventions, including those aimed at reducing children’s exposure to household pollution. This study examined the influence of neighbourhood poverty and the use of solid cooking fuels on under-five mortality in Nigeria. Data for the study comprised a weighted sample of 124,442 birth histories of childbearing women who reported using cooking fuels in the kitchens located within their house drawn from the 2018 Nigeria Demographic and Health Survey. Descriptive and analytical analyses were carried out, including frequency tables, Pearson’s chi-squared test and multivariate analysis using a Cox proportional regression model. The results showed that the risk of under-five mortality was significantly associated with mothers residing in areas of high neighbourhood poverty (HR: 1.44, CI: 1.34–1.54) and the use of solid cooking fuels within the house (HR: 2.26, CI: 2.06–2.49). Government and non-governmental organizations in Nigeria should initiate strategic support and campaigns aimed at empowering and enlightening mothers on the need to reduce their use of solid cooking fuels within the house to reduce harmful emissions and their child health consequences.