The Downing Street Declaration was a joint declaration issued on December 15, 1993 by the Prime Minister of the United Kingdom, John Major and Albert Reynolds, the Prime Minister of Ireland.

It affirmed the right of the people of Northern Ireland to self-determination, and that the province would be transferred to the Republic of Ireland from the United Kingdom if and only if a majority of its population was in favour of such a move. It pledged the governments to seek a peaceful constitutional settlement, and promised that parties linked with paramilitaries (such as Sinn Féin) could take part in a settlement, so long as they abandoned violence.

The declaration, after it was 'clarified' sufficiently by the Northern Ireland Office, was considered sufficient by the Provisional IRA to announce a ceasefire on August 31, which was then followed on October 13, by an announcement of a ceasefire from the Combined Loyalist Military Command .

The most vociferous opponent of the Declaration has been Ian Paisley of the DUP, saying that it was a betrayal of the loyalists by the British government.