Education and Chalmers qualified in medicine in the mid-1960s, and then practised as a clinician in the United Kingdom and two years (1969-1970) in the Gaza Strip. In the mid-1970s, he became a full-time health services researcher with a particular interest in assessing the effects of care. Between 1978 and 1992, he was the first director of the National Perinatal Epidemiology Unit in Oxford.
The National Health Service Research and Development Programme supported extending the approach to other areas of health care.
In 1992, Chalmers was appointed director of the United Kingdom Cochrane Centre, leading to the development of the international Cochrane Collaboration. Subsequently, he became founding editor of the, which documents the history and evolution of fair trials of treatments, and helped to establish the James Lind Alliance, a non-profit organization that "aims to identify the most important gaps in knowledge about the effects of treatments".
The Library has established strategic agreements with international and non-profit organizations to disseminate its publications to a broad international and multilingual audience. Chalmers inspired champions all over the world leading to the development of the Cochrane Collaboration and by 2011 this collaboration had nearly 30,000 volunteers contributing towards summarising research evidence to improve health.
His contributions have been instrumental in advancing international policies on research for health -such as PAHO"s Policy on Research for Health, and to promote a better understanding of the importance of building bridges between users and producers of research for health policy and health care delivery.
Chalmers continues to promote better research for better health care by increasing public appreciation of good research through Testing Treatments interactive and the, and by working with others to reduce waste in research.