His Majesty's Declaration of Abdication Act 1936 was the Act of the British Parliament that allowed King Edward VIII to abdicate the throne, and passed succession to Prince Albert, Duke of York. Edward VIII abdicated in order to marry his lover, Wallis Simpson after facing opposition from the government of the UK and the British dominions (See Abdication Crisis of Edward VIII). Although Edward VIII had signed a declaration of abdication the previous day, he was still King until he gave royal assent to this Act.

The Act was passed through the Houses of Parliament in one day, with no amendments. The governments of the British dominions (then composed of Canada, Australia, The Union of South Africa, New Zealand, and Newfoundland) gave their permission for the Act to apply in their respective realms, a requirement of the Statute of Westminster 1931. However the Act did not apply to the Irish Free State, which instead passed the External Relations Act, recognising the Duke of York as King.

The Act was necessary for two main reasons.

• Firstly, there is no provision in British Law for the sovereign to abdicate. The Act of Settlement 1701 ensured that the senior descendant of the Electress Sophia of Hanover was sovereign in England. The Act of Union 1707 confirmed this for Great Britain. Thus the senior descendant of Sophia is automatically sovereign, whether they wish to be or not. In order for the sovereign to abdicate, Parliament must give its permission.

• Secondly, the Act ensured that the throne passed over to Prince Albert, Duke of York, but that it did not exclude other descendants of the Electress Sophia from the line of succession. Any future descendants of Edward VIII would however, not have a claim to the throne and would not be bound by the Royal Marriages Act 1772.

As soon as King Edward VIII gave his royal assent to this Act, he was no longer King of the United Kingdom of Great Britain and Northern Ireland. The throne immediately passed to Prince Albert, Duke of York, who was proclaimed George VI the next day at St James's Palace, London.