The prevalence of anxiety and depressive symptoms in young people have increased in many countries around the world. Web-based mental health interventions (or W-MHIs) have the potential to reduce anxiety and depression symptoms for young people. Although W-MHIs have become more widely used by young people since the coronavirus disease 2019 (COVID-19) pandemic, real-world engagement in these W-MHIs has remained low compared with engagement reported in research studies. Moreover, there are limited studies examining factors influencing engagement with W-MHIs in the post-COVID-19 pandemic years. This study aims to explore barriers and facilitators of engagement with W-MHIs for anxiety and depression among young people. Seventeen semi-structured interviews and one focus group with three participants were conducted online via Zoom between February and March 2023. Participants were young people aged 18-25 years who had self-reported experience of anxiety and/or depression in the past 6months, lived in Australia, and considered using W-MHIs to manage their anxiety and/or depression symptoms. Inductive thematic analysis was performed to understand the key barriers and facilitators of young people's engagement with W-MHIs. Both individual- and intervention-related factors influenced young people's engagement with W-MHIs. Facilitators of engagement included personal trust and beliefs in W-MHIs, ability to contact a health professional, programme suitability (e.g., affordability, content aligning with user needs), programme usability (e.g., user interface), and accessibility of the online platform. Barriers included concerns about online security, lack of human interaction and immediate responses from health professionals (if any), and negative experience with mental health programmes. Participants expressed greater willingness to pay if they could contact health professionals during the programme. Better promotion strategies for mental health and W-MHI awareness are needed to increase the perceived importance and priority of mental health interventions among young people. Young people should be involved in the W-MHI co-design to enhance the programme suitability and usability for young people, fostering their engagement with W-MHIs.