In January 1999, he joined three of the four other UKUP Assembly members in forming the Northern Ireland Unionist Party.
He acted as whip for the new group, and was selected to stand for Westminster under his new party label at the 2000 South Antrim by-election, but withdrew during the campaign, calling on his supporters to back the Democratic Unionist Party candidate William McCrea.
He did stand for the South Antrim seat at the 2001 general election, but came bottom of the poll, with only 972 votes.
At the 2003 Assembly election, Boyd was able to take only 774 votes, and lost his seat, along with all his party colleagues.
Boyd later joined the Traditional Unionist Voice (TUV), and stood for the party in the 2019 Northern Ireland local elections, where he unsuccessfully contested the Three Mile Water DEA on Antrim and Newtownabbey Borough Council.