The post Brexit deal between UK and European Union would take effect at 11pm on Thursday night after it was signed into law.
The British parliament overwhelmingly backed the agreement in a high-speed process on Wednesday, following the two sides reaching agreement on Christmas Eve.
The UK leaves the EU’s single market and customs union, but the deal ends the possibility of tariffs on goods.
PM Boris Johnson thanked MPs and said: “The destiny of this great country now resides firmly in our hands.”
But opponents say the country will still be worse off than it was while in the EU.
Brexit happened on 31 January, but the UK has continued to follow Brussels’ trade rules until now.
The 1,240-page post-Brexit deal – reached just before the deadline to do so – sets out a new business and security relationship, following the severing of these ties.
It comes four-and-a-half years after the UK voted to leave the EU in a referendum.
The law means that the UK and the EU can continue to trade without extra taxes being put on goods. Although it’s a trade deal that has been agreed, there will be changes to how people travel between the EU and UK, and to the way they live and work.