Lower income households are at greater risk of food insecurity and poor diet quality. In high-income countries, food insecurity is associated with higher levels of obesity, and the global cost of living crisis is likely to have exacerbated existing dietary inequalities for people living with obesity (PLWO) and food insecurity. However, there is a paucity of research on the impact of the cost of living crisis on food purchasing and food preparation practices for PLWO and food insecurity. Using an online survey (N = 583) of adults residing in England or Scotland with a body mass index (BMI) of ≥ 30kg/m2, participants self-reported on food insecurity, diet quality, perceived impact of the cost of living crisis, and their responses to this in terms of food purchasing behaviours and food preparation practices. Regression analyses found that participants more impacted by the cost of living crisis reported greater experiences of food insecurity. Additionally, food insecurity was associated with greater use of specific purchasing behaviours (i.e., use of budgeting, use of supermarket offers) and food preparation practices (i.e., use of energy-saving appliances, use of resourcefulness). Exploratory analyses indicated that greater impact of the cost of living crisis and use of budgeting were associated with poorer diet quality, whereas greater use of meal planning was associated with better diet quality. These findings highlight the fragility of food budgets and the coping strategies used by PLWO and food insecurity during the cost of living crisis. Policy measures and interventions are urgently needed that address the underlying economic factors contributing to food insecurity, to improve access to and affordability of healthier foods for all.