May has been under pressure to reveal her strategy for the talks that will set out the future relationship between Britain and the European Union.
In Tuesday's address, she will call for Britain to unite and get behind Brexit, pleading for an end to the "insults" and rancour between Leavers and Remainers, her Downing Street office said.
But newspapers said she would be laying out the path towards a "hard Brexit" -- a strategy likely to infuriate embittered Remain voters even more.
May will spark two years of Brexit negotiations when she triggers the Article 50 departure process by the end of March.
She has been under pressure to reveal her strategy for the talks that will set out the future relationship between Britain and the European Union.
Downing Street would not be drawn on matching reports in several newspapers that she was targeting a "hard Brexit" -- pulling out of the single market, the European customs union and the European Court of Justice, in order to regain control of EU immigration.
The Sunday Times said May would announce that Britain is seeking a "clean and hard Brexit", citing the above points.
"May's triple Brexit blast" was how The Sun put it, saying May will "show she means business by announcing a triple whammy departure from the EU".
The Sunday Telegraph quoted a government source as saying: "She's gone for the full works. People will know when she said 'Brexit means Brexit', she really meant it."
Downing Street would only say the speech would call on Britain to "set aside old divisions, and unite to make a success of Brexit".
While the June referendum on Britain's EU membership split the country -- the Leave campaign won with a 52 percent majority -- most Britons share a vision of a future Britain that is "secure, prosperous, outward-looking and tolerant", said Downing Street.
"Setting out the government's plan for the Brexit negotiations, the PM will highlight the importance of building on common goals -- such as protecting and enhancing workers' rights -- and focusing on a positive vision of Britain outside the EU."
May has revealed little so far on her negotiating position, but has been clear she wants control over immigration from EU countries -- a major issue in the referendum.
May -- who gave lukewarm backing to the Remain campaign -- was to call on all sides to respect the referendum outcome.
However people voted, the public and parliament want the government to "get on with it", while business was planning to make the best of Brexit, she was to say, according to Downing Street.
"Now we need to put an end to the division and the language associated with it -- Leaver and Remainer and all the accompanying insults -- and unite to make a success of Brexit and build a truly global Britain," May was to say.
The speech will take place at Lancaster House, a central London mansion used by the Foreign Office for glitzy diplomatic occasions.
The audience will be comprised of foreign ambassadors, Britain's Brexit negotiating team and other senior officials involved in the EU departure process.
Meanwhile Brexit Secretary David Davis indicated that Britain would consider a transitional arrangement in the divorce talks.
"If it proves necessary, we have said we will consider time for implementation of new arrangements," he wrote in The Sunday Times.
"We don't want the EU to fail, we want it to prosper politically and economically, and we need to persuade our allies that a strong new partnership with the UK will help the EU to do that," he added.
The EU's chief Brexit negotiator Michel Barnier warned Saturday the bloc must be aware of the risk to financial stability during what are expected to be very tough talks with Britain.