In Northern Ireland, the current main legal framework for compulsory intervention is the Mental Health (Northern Ireland) Order 1986. It is a traditional mental health law which enables detention in hospital if mental disorder and risk criteria are met. However, under Article 3(2), it states that people should not be detained "by reason only of personality disorder". There has been a process of law reform in Northern Ireland to create a non-discriminatory, comprehensive legal framework for all. This resulted in the Mental Capacity Act (Northern Ireland) 2016. The Act, when fully implemented, will replace the Order for everyone aged 16 and over, which is in contrast to most other countries where there are both mental health and mental capacity laws. Under the new Act there are no specific exclusions so, if a person is unable to make the relevant decision, including if the cause of impairment relates to issues associated with personality disorder, then compulsory intervention is allowed as long as the proposed intervention is in the person's 'best interests'. The Act was partially implemented in 2019 and currently is only used when the Order does not apply. This article explores: the development of this new legal framework; the implementation of the Act; and some of the ongoing debates, and practice complexities, related to services for people with a diagnosis of personality disorder.