Dr Thompsell was a GP Principal before retraining in psychiatry and becoming an Old Age Psychiatrist. She has been the Consultant for a multidisciplinary team supporting care homes with nursing and then an old age liaison service in an acute hospital before working in inpatient specialist care. She recently completed 4 years as chair of the Faculty of Old Age Psychiatry at the Royal College of Psychiatrists. 

She was vice chair of the NICE Guidelines development of medicines management in care homes and led on the improving care in dementia workstream for the London Dementia Strategic Clinical leadership group. She was also Clinical Lead for the dementia workstream of the Modernisation Initiative to improve end of life care for those with dementia. 

She is also a medical member of the First-Tier tribunal (Mental Health) for the Ministry of Justice.