Despite the retention of the parliamentary system of divorce for Irish petitioners, divorce law was not static as the changing definition of marital cruelty and precedent established in the divorce court facilitated more Irish parliamentary divorces, especially from female petitioners. The legal definition of marital cruelty evolved from the late 18th century to embrace non-physical violence, the threat of violence and the abuse of children in front of a mother with intent to cause distress. These legal changes were indicative of transformative social mores concerning men’s role in marriage and the marital union more generally. The Irish body of case law pertaining to this shifting definition is explored in addition to the parliamentary divorce of Louisa Westropp, the first Irish woman to divorce whose case established legal precedent in allowing grounds for divorce recognised in the divorce court to be applied to parliament. Contemporaneous reforms in custody rights also impacted and therefore, by the early 20th century, female Irish petitioners were in the majority in bringing divorce bills to Westminster.