The study draws on the resource-based theory (RBT) and the contingency theory to propose why in the context of micro and small businesses (MSBs) in a developing economy, variances in strategic planning (SP) explain significant differences in firm performance and how this effect varies under varying conditions of marketing capability. Survey-based questionnaire data from one hundred and ninety-six Ghanaian MSBs were used to test the study’s hypotheses. Results from moderated regression analysis conducted revealed that SP has significant positive effects on MSBs’ responsive and financial performance and that the financial performance benefit of SP amplifies when marketing capability is high. The study contributes to the SP literature by strengthening and also clarifying the boundaries of the underdeveloped RBT perspective of SP in the context of small businesses. A key implication of the study’s results is that incorporating organizational resource-specific contingency variables could help disentangle the nuances characterizing the SP–performance link.