Urban flooding is emerging as a significant threat to sustainable urban development. While many developed countries have actively documented the impacts of urban flooding and implemented sustainable management practices, such as using the Aqueduct Flood Analyzer, in many developing countries, these impacts remain less documented, and there is limited understanding of the strategies needed to promote sustainable urban development. This paper aims to investigate the current flood situation in Nairobi and Mombasa, Kenya, analyze their detrimental effects on human populations and the environment, and then prescribe strategies for sustainability. The study employed a sustainable development conceptual framework that integrated the case study research design with qualitative data gathered through document content analysis to comprehensively assess the impacts of flooding. Results show that urban floods in Nairobi and Mombasa have significant implications for sustainable urban development, driven by different causes. In Nairobi, heavy bi-modal rainfall, poor drainage systems, and encroachment on riparian land affected over 40,000 residents, causing displacement and property loss. Mombasa's low-lying areas, particularly Likoni and Tononoka, suffer from sea-level rise and poor drainage, with evacuations necessary in flood-prone areas such as Bombolulu. Moreover, both cities face infrastructure damage, loss of life, and environmental degradation. However, mitigation strategies differ, with Nairobi focusing on disaster risk management and Mombasa emphasizing climate-adaptive solutions such as the City Lab initiative. These results imply the necessity of fostering tailored strategies in both cities, addressing their unique flood causes and vulnerabilities while contributing valuable insights to the broader flood management literature on sustainable preparedness.