His intervention, pencilled in for the day that love conquers all, is expected to reach out to MPs who once backed Remain in a bid to bring some peace to the party.
But with the timing set to clash with a Brexit speech from Theresa May and reports that Mr Johnson is being lined up to replace her, one Government source warned it could instead lead to a “Valentine’s Day massacre”.
It comes as Ms May and her senior ministers prepare for two crunch meetings to try and agree a joint-approach to negotiating a final Brexit deal.
It was reported in September that Mr Johnson was persuaded to abandon a speech outlining a harder vision of Brexit shortly before Ms May’s Florence speech, only to then publish the text in a newspaper.
But the speech now earmarked for Valentine’s Day is expected to take a more emollient approach, extending an olive branch to Conservatives on the party’s liberal wing.
The Independent understands that the “liberal Brexit” speech had been due this week, but was postponed ahead of the meetings of the cabinet sub-committee on EU withdrawal.
One source familiar with the speech said no date had yet been totally locked in, but that it would almost certainly be this month.
If the Valentine’s Day plan goes ahead, it could see the Foreign Secretary steal the limelight a few days before the Prime Minister is set to make her own security-themed Brexit speech in Munich.
Mr Johnson and others on the Tory benches are said to be worried that Ms May’s Brexit vision is not yet optimistic enough.
News of his speech also comes after Brexiteers have become increasingly aggravated in recent weeks at suggestions that Ms May is planning to keep the UK inside a form of customs union with the EU – potentially threatening Britain’s ability to have an independent trade policy after withdrawal.
While Downing Street has made clear it is seeking an “end state” deal that will allow the UK to sign new trade deals with other countries, reports have emerged of plotting from the right of the party to replace her if she goes back on her word.
Under one alleged scheme that emerged at the weekend, Ms May would be replaced by Mr Johnson, with Environment Secretary Michael Gove as his deputy PM and the increasingly strident Jacob Rees-Mogg MP as his chancellor. Mr Rees-Mogg is said to have already demanded Ms May sack her civil service Brexit negotiator Oliver Robbins.
Last night, former minister Anna Soubry – a key voice backing a softer Brexit – demanded the Prime Minister stand up to the likes of Mr Johnson and Mr Rees-Mogg, and threatened to walk out if she failed to.
A Government source said: “The speech is being pitched as a bid to unify the party.
“But with the way things are, it could easily end up as a Valentine’s Day massacre.”
The comment refers to the infamous gangland murders on 14 February 1929, which saw Al Capone cement his power over rival groups in prohibition-era Chicago.
Ministers who lean towards a softer Brexit – including Chancellor Philip Hammond, Home Secretary Amber Rudd and Business Minister Greg Clarke – will also attend, with the two sides hoping to reach an agreement on how much the UK should diverge from the EU in the future.
There is then expected to be a further “away day” during the recess where ministers hope to finalise the position.
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies