The resilience of enterprises in sub-Saharan Africa is critically tested by persistent structural constraints, including infrastructural deficits, regulatory complexities, and limited access to finance. Understanding how firms navigate these challenges through strategic adaptation remains a pivotal research gap, particularly in longitudinal and comparative contexts. This study aims to compare the adaptive strategies and resilience outcomes of formal and informal enterprises within a specific East African nation, analysing how differing organisational structures influence capacity to withstand and evolve amidst systemic constraints. A longitudinal comparative case study design was employed, utilising a mixed-methods approach. Data were synthesised from in-depth executive interviews, archival policy analysis, and financial performance metrics across a stratified sample of enterprises from manufacturing, trade, and service sectors. A key divergence was observed: informal enterprises demonstrated superior tactical agility in supply chain reconfiguration, whereas formal enterprises leveraged strategic partnerships for market access. Notably, over 60% of resilient formal firms had institutionalised continuous environmental scanning, a practice largely absent in the informal cohort. Enterprise resilience is not uniformly determined by formality but is co-constituted by the strategic integration of adaptive routines with the specific structural constraints encountered. The study challenges monolithic views of business adaptation in emerging economies. Policymakers should develop tiered regulatory frameworks that recognise and support the distinct adaptive pathways of different enterprise types. Business support programmes must move beyond generic training to foster embedded strategic foresight capabilities. Strategic adaptation, organisational resilience, structural constraints, informal economy, comparative case study, East Africa This paper provides a novel, empirically grounded typology of enterprise resilience strategies, derived from a unique longitudinal dataset tracking adaptive behaviours across formal and informal sectors.