He used the meeting to tell the diplomat of his intention to reject any deal that fails six tests set by his party.
But Brexit campaigners attacked his intervention as a fresh attempt to undermine the country’s negotiating position in his drive to bring down Theresa May’s Government.
Former Ukip leader Nigel Farage, a leading figure in the Leave Means Leave campaign, said the meeting “was clearly an attempt to undermine negotiations after he promised to vote down May’s deal”, adding: “He is obviously believed by the European Commission to be a useful idiot. But I’m sure workingclass people who voted Leave will feel betrayed and angry at his ill thought-out strategy to betray British interests.”
Tory MP Ben Bradley added: “We’ve see this week that Corbyn and Labour want us to continue to take EU rules and pay in through a customs union, or even hold a new vote if they can get away with it.
“Corbyn’s involvement in these discussions behind closed doors can be of no benefit to Britain and only serves to further complicate an already difficult negotiation.
“If he can’t get on board and back the UK in these talks, he should stay out of it.”
A Government source described Mr Corbyn’s visit to Brussels as “unhelpful”.
The Labour leader said they had an “interesting, useful discussion” but admitted the EU diplomat had offered “no opinion” on the opposition’s Brexit plans.
Earlier, Mr Corbyn spoke at a ceremony to name a Brussels square after murdered Labour MP Jo Cox, who had lived in the city for six years before arriving at the Commons.