Following a career in hospital medicine, since 1989 Mackay has been the executive director of the Hong Kong–based Asian Consultancy on Tobacco Control.

[4] From 2006 to 2020 she was Senior Advisor, Vital Strategies, part of the Bloomberg Initiative to Reduce Tobacco Use in Low and Middle-income countries.

She feels passionately about converting health statistics into maps and graphics, and has authored or co-authored 12 atlases, most published by Myriad Editions.

[9] In 2015 she received an honorary degree, Doctor of Social Sciences honoris causa, from Hong Kong Shue Yan University.

In 2016 she received an honorary degree, Doctor honoris causa, from the University of Edinburgh, Scotland, her alma mater.