BELFAST, Northern Ireland — Protestant leader Ian Paisley, who spent decades refusing to cooperate with Northern Ireland's Catholic minority, was elected Tuesday to oversee a power-sharing administration alongside his longtime Sinn Fein foes.

The unopposed election of Democratic Unionist Party chief Paisley, 81, as "first minister" of a new 12-member administration heralded an astonishing new era for Northern Ireland.

Paisley immediately affirmed an oath pledging to cooperate with Catholics and the government of the neighboring Republic of Ireland — moves that the evangelical firebrand long denounced as surrender.

Seconds later Sinn Fein deputy leader and ex-IRA commander Martin McGuinness accepted the No. 2 post of deputy first minister. McGuinness, 56, affirmed the same oath, which required all ministers to support the Northern Ireland police and British courts — a position that Sinn Fein refused for decades.

Within a few more minutes, all 12 power-sharing positions were filled on the basis of how many seats each party holds in the Northern Ireland Assembly.