In the face of growing human needs caused by rapid population growth and urbanization, promoting happiness is increasingly emerging as a feasible way to enhance the achievement of holistic, sustainable development. While many studies have explored happiness at various levels in developed countries, little attention has been paid to the discourse on happiness in developing countries. This study aimed to contribute to a better understanding of the strategies needed to promote happiness and sustainable development in Nairobi and Wajir Counties, Kenya. A case study approach and literature review using document-content analysis were used to evaluate secondary data from online sources. The reviewed key documents included policy papers and reports on sustainable development. For the first time, the happiness evaluation applied the World Happiness indices to the selected cases by categorizing the findings into six main thematic areas-gross domestic product, life expectancy, generosity, social support, freedom, and corruption-for each case to understand the strategies needed to enhance holistic happiness and sustainable development. The study results revealed that pursuing happiness and sustainable development requires a delicate balance between socio-cultural and economic factors. In addition, while progress is evident in Nairobi, addressing corruption is crucial, and Wajir faces slow progress with a pressing need to combat corruption. This study suggests that explicitly incorporating happiness goals into key development planning documents is vital to Kenya's holistic and sustainable societal progress. Incorporating happiness goals into Kenya's development plans is crucial for fostering holistic and sustainable societal progress. By prioritizing well-being alongside traditional metrics, stakeholders and policymakers can ensure policies align with citizens' needs, promoting inclusive growth and long-term prosperity.