It also provided a mechanism for a further amendment to the Constitution upon a declaration by the government on the implementation of the Agreement, most notably by changing Articles 2 and 3 from the previous claim over the whole island of Ireland to an aspiration towards creating a united Ireland by peaceful means, "with the consent of a majority of the people, democratically expressed, in both jurisdictions in the island".

The Government declaration envisaged by the Nineteenth Amendment was made on 2 December 1999, bringing the changes to Articles 2 and 3 and certain other parts of the constitution into effect.

2° Any institution established by or under the Agreement may exercise the powers and functions thereby conferred on it in respect of all or any part of the island of Ireland notwithstanding any other provision of this Constitution conferring a like power or function on any person or any organ of State appointed under or created or established by or under this Constitution.

He claimed the bill was invalid because it purported to allow a mechanism to amend the Constitution by government declaration rather than by referendum.

[3] The referendum returning officer certified the result in the High Court, which notified the Oireachtas, and the Nineteenth Amendment of the Constitution Act 1998 was signed into law by the President on 3 June 1998.

The British-Irish Agreement Act 1999 served in Irish law to ratify the treaty and establish the associated cross-border institutions.

Political disagreements within Northern Ireland meant that establishment would not take place by the deadline of 2 June 1999, so the Oireachtas rushed through a 12-month extension ("such longer period as may be provided for by law" in Article 28.7.5°).