Background and Objective: With their increasing provision of childcare, grandparents are playing an important role in shaping the nutrition environment and eating behaviours of their grandchildren. Despite this, research assessing the feeding practices of grandparents and their association with the dietary quality of the food consumed by grandchildren is limited. Such research is needed to inform the development of interventions that provide tailored guidance to grandparents on adaptive ways of interacting with their grandchildren in the context of mealtimes. Accordingly, the present study sought to examine the feeding practices adopted by grandparents and the association between these feeding practices and grandchild consumption of healthy and unhealthy foods. Methods: In total, 1076 grandparents (60% female; average age = 65.07 years) who reported providing regular childcare to at least one grandchild aged 3 to 14 years were recruited. They completed an online survey assessing a variety of constructs including their feeding practices and the frequency with which their grandchild consumes specific foods and beverages while in their care. Results: Grandparents reported using positive feeding practices such as ‘encouragement of balance and variety’ more frequently than negative feeding practices such as ‘control over eating’. Positive feeding practices were found to be more important correlates of diet quality than negative feeding practices, with the provision of a healthy food environment and limit setting emerging as the most important practices associated with healthy eating. Conclusions: Grandparents are having a demonstrable impact on the dietary behaviours of their grandchildren and should be considered in initiatives promoting healthy lifestyle behaviours in young children. To prevent poor diet and support consumption of fruit and vegetables, grandparents should be encouraged to increase the availability of healthy foods in their home and set limits on unhealthy foods.