The Legitimacy Act 1959 (7 & 8 Eliz. 2. c. 73) was an Act of the Parliament of the United Kingdom. It was repealed by the Family Law Reform Act 1987.^[1]

Prior to the passing of the Act, legitimacy was governed by the Legitimacy Act 1926. Under that act, the marriage of a child's parents after its birth did not legitimise it when one of the parents was married to a third person at the birth of the child.^[2] Although the Royal Commission on Marriage and Divorce recommended keeping this on the statute books by a vote of twelve to seven, Section 1 repealed this and allowed a child to be legitimised when his parents married, regardless of their past status. This was retroactive; if a child's parents were married when the Act came into force, the child was legitimised.^[3]

Section 2 legitimised the children born of void marriages, provided that both or either parents reasonably believed that the marriages were valid and entered into in good faith (such as a marriage below the age of consent, where both wife and husband believed they are above it).^[4][5] Section 2(3) of the Legitimacy Act 1959 provided also that section 2 applied only where the father of the child was domiciliated in England.