[9] From 2013 to 2022, he was the longest-serving dean of medicine at the University of Hong Kong, where he was also the inaugural Helen and Francis Zimmern Professor in Population Health.

[12] His family moved to Canada when he was 13[13] in Form 2[14] (equivalent to Year Eight in England, Wales, Australia and New Zealand), due to his father's job with a multinational company,[15] Leung undertook his undergraduate education at the University of Western Ontario, majoring in chemistry and minoring music.

[1][20] In 2013, Leung was appointed as the 40th dean of the HKU Li Ka Shing Faculty of Medicine and chair professor of public health.

[39] Leung resigned as dean in November 2021 to succeed Leong Cheung at the Hong Kong Jockey Club as the executive director (charities and community).

[43][44] He is currently serving on the Steering Committee on Primary Healthcare Development of the Government of Hong Kong since 2017,[45][46] the board of directors of the Laboratory of Data Discovery for Health at the Hong Kong Science Park since 2020,[1][47] the board of governors of the Wellcome Trust since 2021,[48] and the Global Health Risk Framework Commission.

[49] During the COVID-19 pandemic, Leung is one of the experts advising the chief executive and the Government of Hong Kong,[50] even after leaving HKU.

[1][55] Leung is an ex-officio member of the Medical and Health Services subsector of the Election Committee of Hong Kong for the 2021–2026 term.

All principal officials of Hong Kong, including the secretaries for the Bureaux, must be filled by Chinese citizens without the right of abode in foreign countries.

[69][70] On a press conference about the COVID-19 pandemic on 25 January 2020, Leung and attending government officials asked the public to wear face masks but did not do so themselves.