The Prime Minister landed and walked through the doors of the Berlaymont building, the Headquarters of the European Commission in Brussels.
He refused to answer questions from reporters but did say “Hello, how do you?” as he clutched his red despatch box.
As the two leaders posed for the cameras, the Prime Minister asked Ms von der Leyen if they were taking their masks off.
The EC president agreed, but told Mr Johnson to “keep distance” as they briefly removed their face coverings.
Ms von der Leyen added: “Then we have to put it back on. You have to put it back on immediately.”
The Prime Minister responded, saying: “You run a tight ship here, Ursula, and quite right too.”
The pair then headed off for dinner as talks on a post-Brexit trade deal remained on a knife-edge.
Fish has proved one of the most difficult parts of a Brexit trade deal to swallow for the negotiating teams, but it was served to Boris Johnson on a plate during crunch talks in Brussels.
The Prime Minister dined on a starter of scallops and a main course of steamed turbot when he met with the European Commission president Ursula von der Leyen.
The two leaders were joined by their chief negotiators and officials for the three-course dinner at the Berlaymont building aimed at breaking the deadlock in the protracted trade deal talks.
Negotiations have faltered on fishing rights, among other issues, and the Commission’s menu will be seen as a pointed gesture by some but a sign that it has a sense of humour by others.
Mr Johnson and Mrs von der Leyen were served pumpkin soup and scallops to start, followed by a main course of steamed turbot, mashed potatoes with wasabi and vegetables.
For pudding they ate pavlova with exotic fruit and coconut sorbet, but the Commission stopped short of serving another popular meringue-and-cream dessert, the Eton Mess, believed to originate from the Prime Minister’s alma mater.
The Prime Minister appeared in jovial spirits as he waved to photographers as he left Downing Street before stepping into a blacked-out car with UK Chief Brexit negotiator David Frost on Wednesday afternoon.
Boris Johnson tweeted a picture of himself boarding the plane, saying: "A good deal is still there to be done. But whether we agree trading arrangements resembling those of Australia or Canada, the United Kingdom will prosper mightily as an independent nation.”
Mr Johnson had earlier said no prime minister could accept the demands the European Union is currently making as the price for a trade deal.
He was flying to Brussels for dinner with European Commission president Ursula von der Leyen with the negotiations in crisis.
Time is running out to reach a trade agreement before the current transitional arrangements expire at the end of the month, but Mr Johnson insisted a deal was still possible.
At Prime Minister’s Questions Mr Johnson set out the main problems he has with the EU’s position, although he said “a good deal is still there to be done”.
The protracted negotiations on a UK-EU trade deal have faltered on the issues of fishing rights, the “level playing field” measures aimed at preventing the UK undercutting the EU on standards and state subsidies, and the way that any deal would be governed.
Mr Johnson said: “Our friends in the EU are currently insisting that if they pass a new law in the future with which we in this country do not comply or don’t follow suit, then they want the automatic right to punish us and to retaliate.
“Secondly, they are saying that the UK should be the only country in the world not to have sovereign control over its fishing waters.
“I don’t believe that those are terms that any prime minister of this country should accept.”
He again insisted the UK would “prosper mightily” with or without a deal – a claim which has been disputed by economic experts including the Office for Budget Responsibility and the governor of the Bank of England.
Failure to reach agreement would see tariffs imposed on UK exports to the EU, the country’s biggest trading partner, and could also increase bureaucracy.
The Office for Budget Responsibility has suggested that a no-deal outcome could wipe two per cent off gross domestic product, a measure of the size of the economy, in 2021.
The Bank’s governor Andrew Bailey has warned that the long-term damage caused by a no-deal situation would be worse than the economic hit from coronavirus.
Mr Johnson’s press secretary Allegra Stratton told reporters: “The Prime Minister is going to be clear this evening that he cannot accept anything that undermines our ability to control our laws or control our waters.
“He is going to put that clearly to von der Leyen and see what her response is.”
The Prime Minister did not speak to reporters as he left Downing Street to head to the Belgian capital.
Mr Johnson is expected to arrive for the dinner at 7pm UK time, with negotiators Lord Frost and Michel Barnier also attending the event.
Labour leader Sir Keir Starmer suggested his MPs would back a deal if Mr Johnson brought one back to the Commons.
Reporting by PA