[1] Barrow was appointed as Permanent Representative in January 2017 following the resignation of his predecessor, Ivan Rogers, and played an important role in the United Kingdom Brexit negotiations.

He took up the post in July that year and held it until 2008 when he returned to Brussels as UK Representative to the Political and Security Committee and Ambassador to the Western European Union.

However, this masked some significant achievements that he made in a tenure marked by Russian military interventions in Ukraine and Syria and a crackdown on dissent by Vladimir Putin.

"[8] After leaving his role in Moscow, Barrow was appointed as a political director at the Foreign Office in London, succeeding Simon Gass.

A Downing Street spokesman said Barrow was "a seasoned and tough negotiator, with extensive experience of securing UK objectives in Brussels.

"[9] Charles Crawford, who worked with Barrow in the early 1990s, commented that he "understands Brussels and the EU, but he is not pickled in its ghastly processes.

"[11] The Financial Times reported that Barrow's appointment was opposed by Oliver Robbins, the permanent secretary at the Department for Exiting the European Union, who wanted to take control of negotiations with the EU himself.

[13] On 20 March, Barrow appeared before the European Scrutiny Committee to give evidence on UK-EU relations prior to the invocation of Article 50.

During the hearing, he warned that it may not be possible to leave the European Union without paying anything, as some Conservative MPs had suggested, and that "other legal opinions" offered "a different interpretation".

[19] After the UK left the EU on 31 January 2020, Barrow's portfolio changed to British Ambassador to the European Union effective 1 February, being succeeded in 2021 by Lindsay Croisdale-Appleby.