The COVID-19 pandemic threatens the food security of people in low-income countries. This is important for people living with HIV (PLWH) because HIV medication should be taken with food to avoid side-effects. We used survey data (n = 314) and qualitative interviews (n = 95) to longitudinally explore how the pandemic impacted food insecurity among PLWH in Kampala, Uganda. Prior to March 2020, 19.7% of respondents were food insecure. Our regression models estimate that food insecurity rose by 9.1 percentage points in our first round of surveys (June–September 2020; p < 0.05; t = 2.17), increasing to 17.2 percentage points in the second round of surveys (July–November 2021; p < 0.05; t = 2.32). Qualitative interviews reveal that employment loss and deteriorating support systems led to reduced meals and purchasing of cheaper foods.