The Protestant Unionist Party (PUP) were a political party operating in Northern Ireland from 1966 to 1971. They are the forerunner of the modern Democratic Unionist Party (DUP) and emerged from the Ulster Protestant Action (UPA) movement, changing to the PUP in 1966.

The UPA had two councillors elected, and in 1967 both were successfully re-elected as PUP candidates. They stood six candidates against moderate Ulster Unionist Party members of the Stormont parliament in the 1969 election and polled over 20,000 votes.

When Terence O'Neill (the then Northern Irish Prime Minister) stood down from Stormont in 1970 along with one of his colleagues, the PUP nominated candidates for the two vacant seats (Ian Paisley and William Beattie, PUP leader and deputy respectively). Both were successfully elected to Stormont and in that years general election, Paisley was elected to represent Antrim North in Westminster.

The PUP campaigned for the retention of the union, preferential treatment for Protestants in employment, and for total freedom for Orange parades. The PUP was wound up in 1971 and re-emerged as the DUP in October of that year.

Later in the 1987 general election, George Seawright, a former DUP candidate, defied an official pact between the Unionist parties and revived the Protestant Unionist label for his candidature.