Theresa May will strike a conciliatory tone as she invokes Article 50 this afternoon, offering a partnership with the rest of the European Union and imploring Britain to "come together".
The Prime Minister will formally launch the process for the UK to leave the European Union in a letter that will be hand delivered to European Council President Donald Tusk at around 12.30pm.
After marking out hard lines on future payments to the European Union and the influence of EU law after Brexit, the text of the Prime Minister's letter is expected to offer some room for manoeuvre in negotiations.
Addressing MPs in the Commons as the letter is delivered, Mrs May will vow to "represent EU nationals who have made this country their home".
She will not comply with the wishes of her Brexiteer backbenchers who wanted to name the Article 50 date as a cut off for newly-arrived EU citizens to gain rights such as permanent residence.
Some Conservative MPs are concerned about a surge in the number of EU migrants.
However, on Tuesday the European Commission, Council and Parliament signalled that "EU law must apply until Brexit day" in two years' time.
The European Parliament, which can veto an UK-EU deal, is next week expected to make the guarantee of full EU citizen rights a red line.
After meeting with representatives of EU citizens living in the UK, European Commission Brexit negotiator Michel Barnier said the EU will be "firm on their rights".
Meanwhile, Mrs May's promise to "end the jurisdiction" of the European Court of Justice in the UK is being recalibrated as ending "direct jurisdiction".
This could allow a different court to offer an intermediary role as arbiter for EU law issues applying to UK firms seeking maximum single market access.
On the so-called "divorce bill" reported on by Sky News at the December EU summit, the Prime Minister has ruled out large yearly payments, but that still allows for a one-off settlement of net liabilities.
Mrs May signed the Article 50 letter in the Cabinet room on Tuesday afternoon, overseen by a picture of the first British Prime Minister Robert Walpole.
Later, she called Mr Tusk, European Commission President Jean-Claude Juncker and German Chancellor Angela Merkel
During her address in the Commons, Mrs May will call on the UK to "come together" and "no longer be defined by the votes we cast in the referendum".
She will vow to "represent every person" in the negotiations, adding that she has a "fierce determination" ahead of a "momentous journey" for a country that is "one great union of people and nations...with a bright future".
Mr Tusk is expected to hold a press conference responding to the letter this afternoon.