MPs passed the European Union (Croation Accession and Irish Protocol) Bill on 27 November 2012, approving it at third reading without a vote.
The bill approves the Republic of Croatia joining the European Union in July 2013, in line with a treaty signed at Brussels on 9 December 2011.
It also includes the protocols to the Lisbon Treaty put forward by the Czech and Irish governments, and plans to maintain the number of EU commissioners at one per member state.
The terms under which Croatian nationals can enter the UK labour market are also set out in the bill.
MPs backed the bill at second reading on 6 November without a vote, despite reservations from some Conservative backbenchers.