Excessive sedentary behaviour is associated with negative individual functioning. This study explored associations between personality traits and two measures of sedentary behaviour. In total, 504 young Australian adults (382 women, 122 men; Mage = 20.41 ± 5.12 years) completed measures of personality, physical activity, sitting time, television viewing, and electronic gaming. After controlling for age, sex, and physical activity levels, we found that extraversion was negatively associated with total sitting time, and that both extraversion and conscientiousness were negatively associated with leisure time screen time (television viewing and electronic gaming). No moderation effects were observed for age, sex, or physical activity. These findings provide evidence that personality is important for adult sedentary behaviour, and that sedentary behaviour measurement (total sitting time or leisure time screen time) is an important consideration in personality–sedentary behaviour research.