Boris Johnson has described the signing as “a fantastic moment” which would bring an end to more than three years of “argument and division” since the referendum vote to leave the EU in 2016.
The step forward in the path towards Brexit came as the PM faced challenges on the domestic front - being urged to scrap HS2 by a group of 13 Tory MPs while his business secretary Andrea Leadsom met with the family of Harry Dunn to discuss the ongoing effort to bring Anne Sacoolas back to the UK to face justice.
Meanwhile the passing of Good Friday architect and former Stormont deputy first minister Seamus Mallon prompted tributes from across the political spectrum. Tony Blair, who worked with him to bring peace to Northern Ireland, said he was "Brave, blunt...someone deeply respected and admired across the troubled landscape of Irish politics"
And in Labour leadership contest news, Len McClusky's union Unite expressed its support for Rebecca Long-Bailey to succeed Jeremy Corbyn as Labour leader.
Here are all of the day's events as they happened: