Siew Noi has a Bachelor of Arts (1989) in Social Work from the National University of Singapore and a Master of Science in Family Therapy (1997) from the world-renowned Institute of Psychiatry, King's College London. Subsequently, working under the South London Maudsley NHS Trust, the leading mental healthcare provider in the United Kingdom, she specialised in Systemic Psychotherapy and Family Therapy and, in particular, Child and Adolescent Mental Health and Eating Disorders. She is a United Kingdom Council of Psychotherapists (UKCP) recognised psychotherapist and is currently a member of the Association for Family and Marital Therapy (Singapore).
On returning to Singapore in 2001, Siew Noi founded her private practice, Psychotherapy Works, providing family therapy specialising in child and adolescent mental health, marital/couples therapy, and individual psychotherapy. She has also been actively involved in training and supervising Family Therapists, Marital Therapists (or Marriage Therapists), Marriage Counsellors, School Counsellors, and Social Workers for local and international universities and training centres, including the National University of Singapore, Nanyang Technology University, King's College London and Swinburne University.