As the Eurocrat with powers over financial regulation, he is said to have angered the usually-cool Sir Mervyn King to such an extent that the then Bank of England governor was still shaking with rage an hour after the meeting ended.
His appointment to the role saw him mooted as the “most dangerous man” in Europe in some quarters of the Press and a year after Mr Barnier had taken on the internal market commissioner’s role in Brussels, David Cameron claimed the City was under “constant attack” from EU directives.
Jean-Claude Juncker’s decision to give the former MP and MEP the crucial role as the commission’s chief negotiator for Brexit will be viewed by many as an aggressive move.
The commission president, who has made clear his anger at Britain’s vote to leave the bloc, said he wanted “an experienced politician for this difficult job”.
But Conservative Sajjad Karim insisted the appointment of Mr Barnier is “actually good”. Prime Minister Theresa May “can work with him”, he said, although the MEP admitted he was “not so sure” the key Brexit-backing Cabinet ministers would be able to.
Mr Barnier, 65, always insisted the fears about his role in regulating the City were “unfair and unjust”, telling the Financial Times he had gone into the role wanting to “build a compromise”.
He became involved in French politics as a teenager and later came to prominence after running the successful bid to secure the 1992 Winter Olympics for his country.
A key figure in centre-right politics, he served as minister for the environment, European affairs, foreign affairs and agriculture under presidents Jacques Chirac and Nicolas Sarkozy.
He was named special adviser for defence and security by Mr Juncker last year and released a paper calling on Brussels to “respond to the security imperatives of today and achieve tangible progress in charting a course towards a common Union defence policy for the future”.
Mr Barnier has said he is “honoured” to have been tasked with what will be hugely complex negotiations over Britain’s exit from the EU.
Ministers will be hoping the negotiator will go into his latest role with at least the same intention of “compromise” he said he started out with as a commissioner taking on the City.