This study examined the relationship between the adoption of International Financial Reporting Standards (IFRS), in particular IFRS 9, and the financial performance of a commercial bank, using Stanbic Bank Uganda as the case. A quantitative single-case time-series design was adopted, and a coded dataset of 60 quarterly observations was analysed using descriptive statistics, Pearson correlations, multiple linear regression of return on assets and binary logistic regression of whether return on assets exceeded 3%, supported by diagnostic tests. The study results indicated that return on assets averaged 2.44%, and that the non-performing loans ratio (B = -0.32, p < 0.001), the COVID-19 period (B = -0.93, p < 0.001) and GDP growth were significant determinants, whereas the post-IFRS 9 indicator was not significant (B = 0.18, p = 0.400). The Durbin–Watson statistic indicated positive autocorrelation, and Newey–West standard errors left the conclusions unchanged. The study concluded that, in the study data, apparent changes in profitability after the standard’s introduction were explained by credit quality and shocks and not by the standard itself, and it recommended continued disclosure, capacity building and research on real data.