Background: Physical activity (PA) promotes health and well-being. For students, university represents a transitional period, including increased independence over lifestyle behaviors, in addition to new stressors and barriers to engaging in PA. It is, therefore, important to monitor PA trends in students to gain a greater understanding about the role it might play in physical and mental well-being, as well as other factors, such as attainment and employability. Methods: Cross-sectional surveys were conducted in 2016 in Scottish universities and colleges, and in 2017 in universities and colleges across the United Kingdom, and the data were pooled for the present study (N = 11,650). Cumulative ordinal logistic regression was used to model the association between PA levels and mental and personal well-being, social isolation, and perceptions of academic attainment and employability. Results: Only 51% of the respondents met the recommended levels of moderate to vigorous PA per week. There was a linear relationship between PA levels and all outcomes, with better scores in more active students. Conclusions: UK university students are insufficiently active compared with the general population of 16- to 24-year olds. Yet, students with higher PA report better outcomes for mental and personal well-being, social isolation, and perceptions of academic attainment and employability.