Judith Longstaff Mackay, SBS, OBE, JP, FRCP (Edin), FRCP (Lon) (born 1943 in Yorkshire, England) is a British-born and Hong Kong–based medical doctor and international tobacco control advocate who has led a campaign against tobacco in Asia from 1984 onwards, campaigning for tax increases to discourage youth smoking, for the creation of smoke-free areas, and against tobacco promotion.
Her main interests are tobacco in low-income countries, women and tobacco, and challenging the transnational tobacco companies.