He will describe severing ties with the other 27 EU nations as “a moment of real national renewal and change”.Little will change immediately, as the UK begins a “transition period”.
Most EU laws will continue to be in force – including the free movement of people – until the end of December, by which time the UK aims to have reached a permanent free trade agreement with the EU.
In a statement, Labour leader Jeremy Corbyn urged the country to “build a truly internationalist, diverse and outward-looking Britain'”.
Brexit was originally scheduled for 31 March last year.
To mark Brexit, Mr Johnson will hold a cabinet meeting in Sunderland on Friday morning.