Marilyn Brennan is a senior systemic family psychotherapist working at the Prudence Skynner couples and Family Clinic, a tier 3 and 4 NHS service based at Springfield Hospital, South West London NHS trust, as a tutor on the foundation and intermediate family therapy courses. She has been a tutor on these courses since 2003. From 2002 until her partial retirement in 2016 she worked in the same trust on the Adult National Eating Disorder Service on the inpatient ward, day patient and outpatient clinics. She has also worked privately for a short time at the Nightingale Hospital Marylebone, in the eating disorder service and adolescent inpatient wards and outpatient clinics.

She has been a supervisor for many years and has supervised at Masters level at the Prudence Skynner clinic and the Family Therapy department at the Institute of Psychiatry. Prior to 2002 Marilyn had had a long career in nursing occupying a number of posts from staff nurse to team leader, mainly working in adult services working with survivors of child sexual abuse, self harm and voice hearers.  In 2001 she won a national award for her work with voice hearers. She is an external examiner for Surrey University family therapy courses. She has also been a member of a number of boards within AFT as a national assessor: the Professional Affairs committee, and the Accreditation committee.