Background: A combination of walking, other moderate physical activity, and vigorous physical activity is recommended for achieving good health. Vigorous activity has unique health benefits but may be less accessible to disadvantaged people. To reduce health inequity, we need to understand the differences in physical activity participation among socioeconomic subgroups and whether this is changing over time. Methods: Data from the 2002 to 2015 Adult New South Wales Population Health Surveys (164,652 responses) were analyzed to investigate trends in walking, moderate and vigorous physical activity participation by socioeconomic status as measured by educational attainment. Analysis used age- and sex-adjusted multivariable linear models that accounted for complex survey design. Results: In 2002, the highest socioeconomic group spent 18.5 (95% confidence interval, 8.2-28.8) minutes per week more than the lowest socioeconomic group being vigorously active. By 2015, this gap had steadily increased to 41.4 (95% confidence interval, 27.6-55.1) minutes per week. Inequity between groups was also found for duration of moderate activity but not for time spent walking. Conclusions: Low participation in vigorous activity in the lowest socioeconomic group is likely driving increasing inequities in physical activity and widening participation gaps over time. Barriers preventing the most disadvantaged people in New South Wales from engaging in vigorous activity should be addressed urgently.