In 1970, Beattie was elected to the Northern Ireland House of Commons in a by-election in South Antrim. Beattie stood for Belfast North in the 1970 United Kingdom general election, but came a distant third, behind the Ulster Unionist and Labour candidates. In 1971, the PUP formed the Democratic Unionist Party (Democratic Unionist Party), and Beattie retained his post as deputy leader.
The Parliament was prorogued in 1972, but Beattie was elected to the Northern Ireland Assembly of 1973, and became deputy chief whip of the United Unionist Assembly Party.
He was again elected, to the Northern Ireland Constitutional Convention in 1975, to Lisburn District Council in 1977, and to the Northern Ireland Assembly of 1982. He resigned from the Democratic Unionist Party in the mid-1990s, and retired as a minister on 31 December 2005.
1st Northern Ireland Assembly (1982). 1st Northern Ireland Assembly (1973–1974)]
On the same day, Paisley was elected for Bannside, and the two became the PUP"s first Members of Parliament.