Strong evidence suggests that exercise and eating behaviours are strongly linked. Theory of Planned Behaviour is a theoretical framework that has been successfully used to explain and predict both behaviours. The aim of the present study is to explore the constructs of Theory of Planned Behavior (TPB) that better predicts exercise and healthy eating: a) intentions and b) self- reported behaviors among normal weight and overweight/obese adults. Participants were 361 adults in Greece (women: N = 152). According to their BMI scores, they have been grouped into normal weight and overweight/obese. Data were collected with an online questionnaire assessing variables of the theory of planned behavior (TPB) toward exercise and healthy eating intentions and behaviors. Correlations between the variables of TPB and behaviors (healthy eating and exercise) were higher in the normal weight group than in the overweight/obese group. The strongest predictor of intention to exercise was perceived behavioral control for both groups with the overweight/obese group showing higher values in comparison to normal weight group values. The same associations emerged for the prediction of intention for healthy eating behavior. The attitude was also a statistically significant predictor for both groups with higher values in normal weight group. The strongest predictor of exercise behavior was the intention, whereas for eating behavior significant predictors were attitudes, intentions and perceived behavioral control. TPB framework explained both intentions and behaviors for exercise and healthy eating of normal weight and overweight/obese adults. Initial information on which TPB constructs explain better intentions and behaviors by group implied that normal weight group has more positive exercise and healthy eating attitudes and intentions than the overweight/obese group; the behaviors of the overweight/obese group were explained better by perceived behavioral control. The above information can be used to design more effective interventions that aim to produce changes in both behaviors.