The demand for using library apps to search for information has been increasing after the COVID-19 outbreak. To look into how the pandemic affects the users’ perception of the loyalty of using library apps, we designed this research by amalgamating the updated IS success model and S–O-R model to evaluate the service quality of a public library app under the Hong Kong Government mobile applications initiative. A third-order model is established to demonstrate the multi-faceted aspects of service quality and mediating effects of perceived brand image, satisfaction, and e-word of mouth. Using structural equation modeling, data collected from Hong Kong, a metropolis where mobile services empower its citizens, showed the interrelationships among service quality and possible outcomes (i.e., perceived brand image, user satisfaction, e-word of mouth, and user loyalty). Findings also indicate that the influence of perceived service quality on user loyalty could only be achieved through perceived brand image and user satisfaction. This is a timely study during the COVID-19 pandemic, as the lockdown and social distancing arrangements created challenges for citizens to search for information in public libraries in person. Our findings and suggestions reiterate the importance of considering the usability concepts when analyzing the service quality of each unique app. They also provide insights for practitioners in developing the next generation of apps for smart public information services and call for further investigation into the proposed hierarchical model and other potential factors related to service quality.