Public transport ridership has been steadily increasing since the early 2000s in many urban area in North America. However, many cities have more recently seen their transit ridership plateaued, if not decreased. This trend in transit ridership has produced a lot of discussion on which factors contributed the most to this new trend. While no recent study has been conducted on this matter, understanding the levers that can be used to sustain and/or increase transit ridership is essential. The aim of this study is, therefore, to explore the determinants of public transport ridership from 2002 to 2015 for 25 transit authorities in Canada and the United States using a longitudinal multilevel mixed-effect regression approach. Our analysis demonstrates that vehicle revenue kilometers (VRK) and car ownership are the main determinants of transit ridership. More specifically, the results suggest that the reduction in bus VRK likely explains the reduction in ridership observed in recent years in many North American cities. Furthermore, external factors such as the presence of ridesourcing services (Uber) and bicycle sharing, although not statistically significant in our models, are associated with higher levels of transit ridership, which contradicts some of the experts’ hypotheses. From a policy perspective, this research suggests that investments in public transport operations, especially bus services, can be a key factor to mitigate the decline in transit ridership or sustain and increase it. While the results of this study emphasize that fare revenues cannot support such investments without deterring ridership, additional sources of revenues are required. This study is of relevance to public transport engineers, planners, researchers, and policy makers wishing to understand the factors leading to an increase in transit ridership.