Rejecting the Brexit deal will be risky and lead to "division and uncertainty", Prime Minister Theresa May will say to MPs who oppose her plan.
Her Commons speech comes after the 27 other EU leaders approved the terms of the UK's exit at a summit on Sunday.
Mrs May now has to persuade politicians in the UK Parliament to back the deal.
But cabinet ministers admit she faces an uphill struggle, with Labour, the Lib Dems, the SNP, the DUP and many Tory MPs set to vote against it.
Northern Ireland's Democratic Unionist Party has said it will review its parliamentary pact with the Conservatives - which props up Mrs May's government - if the deal is approved by MPs.
Labour leader Jeremy Corbyn has said his party will oppose the deal, calling it "the worst of all worlds".
The prime minister has pledged to put her "heart and soul" into a two-week push to convince MPs to back the terms of the UK's withdrawal from the EU and its future relations with the bloc.
Parliament will decide whether to accept or reject the package next month, in a vote which is likely to be on 12 December.
Mrs May has said it is the "only deal" on the table for the UK, which is due to leave the EU on 29 March 2019.
Following a two-hour cabinet meeting earlier, No 10 said in the "unlikely event" that Parliament could not agree on the terms of withdrawal "all necessary action" would be taken to prepare the UK to leave without an agreement.
Mrs May's campaign - which saw her appeal to the public in a "letter to the nation" at the weekend - will later see Labour MPs briefed on the deal while there will be a reception for business leaders at Downing Street.
The Daily Telegraph reported Mrs May would challenge Mr Corbyn to a head-to-head debate. Labour says he would "relish" a debate while Lib Dem leader Sir Vince Cable said he would like to join in and "take them both on".
But former Conservative cabinet minister Damian Green said he was sceptical about the idea, telling the BBC's Victoria Derbyshire show it was unlikely to "illuminate" what was a hugely complex subject.
Source: bbc