The former Labour prime minister is being hosted by the Brussels boss at his Berlaymont headquarters in Brussels.
Jean-Claude Juncker’s spokesman confirmed the pair “knew each other well” and both will “discuss the future relationship of the UK and the EU”.
The meeting comes a day after a Supreme Court ruling decided Theresa May will have to gain the approval of MPs before she triggers Article 50.
Tony Blair and Jean-Claude Juncker embrace in Brussels today
Blair and Juncker: Together through the years
Wed, January 25, 2017
Former Prime Minister, Tony Blair and President of the European Commission, Jean-Claude Juncker have always shared a friendly relationship over the years.
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President Juncker has been in politics for 34 years, and the Prime Minister for 19 years
Margaritis Schinas, Jean-Claude Juncker’s spokesman
Mr Blair campaigned for Britain to stay in the Brussels club and even suggested Brexit could be stopped with Britons “entitled to try” to thwart the process.
Chancellor Phillip Hammond, yesterday, laid into the ex-Labour premier saying his failure to negotiate a deal to stop mass migration to Britain in 2004 sparked public unrest in Brussels.
Mr Blair’s spokesman said he would be “holding a number of private meetings, including one with Mr Juncker”.
The meeting is taking place after Mr Blair speaks at the International Holocaust Remembrance Day ceremony in the European Parliament.
Tony Blair was hosted by Juncker in Brussels
Tony Blair and Jean-Claude Juncker are said to know each other well
The pair are set to discuss Brexit
Margaritis Schinas, Mr Juncker’s spokesman, said of the meeting: “President Juncker has been in politics for 34 years, and the Prime Minister for 19 years.
“He is on a personal, friendly relationship with most of the few people who had the chance to serve with him as prime ministers and members of the European Council. The two men know each other well.
“This is an occasion to keep in track and talk to people who have talked an important role in the past, and they are very much covering current European and world affairs.”
Tony Blair campaigned to remain in the EU
He told the Daily Telegraph: “If an objective observer discusses the current EU policy agenda, the issue of the future relationship with the United Kingdom and the European Union is very much part of this agenda.
“But this is not a meeting that will take place on a single issue.
“This is a meeting that a tour d’horizon character that covers everything that matters today in European politics and economics.”