His predecessor Theresa May spent years negotiating a withdrawal agreement with the EU but UK lawmakers rejected it three times, Efe news reported.
Johnson has promised the UK will leave the EU by October 31 "do or die".
He said on Wednesday during his first speech as leader that he will strive for "a new deal, a better deal" but that there is a "remote possibility" of the UK leaving with no deal.
The EU has said that it will not reopen negotiations on the withdrawal agreement.
"The EU will remain attached to the agreement," said the first Vice-President of the Commission, Frans Timmermans.
He also warned that Brexit without an agreement would be a "tragedy" for both sides.
President of the EU Commission Jean-Claude Juncker said he was willing to work with Johnson "in the best possible way".
His counterpart in the European Council, Donald Tusk, congratulated Johnson on his appointment.
He added in a statement on Twitter: "I look forward to meeting you to discuss - in detail - our cooperation."
Michel Barnier, the EU's chief Brexit negotiator, said they will be ready if Johnson pursues a no-deal strategy but it would never be the bloc's choice.
He told the BBC on Wednesday: "We look forward to hearing what the new Prime Minister Boris Johnson wants, what are the choices of the UK.
"Is it an orderly Brexit? This is the choice, the preference of the EU and we have worked for an orderly Brexit all along the last three years.
"Is it a no-deal Brexit? A no-deal Brexit will never be, never, the choice of the EU. But we are prepared."
Barnier took part in a meeting on Wednesday held by the Brexit monitoring group in the European Chamber, following the UK's change of leadership.
The European Parliament said in a statement that an "orderly exit" is in the "overwhelming interests of both parties".
It reiterated that the withdrawal agreement will not be reopened and warned that statements made during the Conservative Party leadership race had increased the risk of a "messy" brexit which would be harmful for the economy.
( With inputs from IANS )