Sian worked at the Nuffield Trust as a senior public health trainee from August 2010 until September 2011. She has held training positions at West Kent PCT, Southwark PCT and South East London Health Protection Unit. Previously Sian worked as a general coordinator for Medecins du Monde, setting up an antiretroviral treatment programme in a regional hospital in Tanzania, one of the first of its kind. She has also worked in local government leading on a variety of transport projects and in medical research. She has an MSc from the London School of Hygiene and Tropical Medicine.
Whilst at the Trust Sian worked on the prioritisation of health care in the NHS, patterns of health and social care at the end of life and trends in admissions for ambulatory care sensitive conditions.