In a preview of her speech to be delivered on the opening day of the party’s virtual spring conference, Ms Davidson will urge pro-UK voters to unite behind the Scottish Tories to derail the SNP’s push to achieve a majority at the election on May 6.
Her pledge comes after a poll carried out by Savanta ComRes for The Scotsman showed the SNP narrowly missing out achieving a majority at Holyrood.
The poll, published on Thursday, was also the second survey in the past week to show a lead for No should a Scottish independence referendum be held tomorrow.
However, Ms Davidson has previously made a similar declaration on the decline in support for the SNP and independence.
In 2016, the-then Scottish Tories party leader declared "peak Nat had passed”, similarly claiming the SNP’s powers were on the wane. The ruling party in Scotland would go on to win 48 of a possible 59 seats for Scotland in Westminster at the 2019 general election.
Ms Davidson will say this afternoon: “In two weeks’ time we will enter the official campaign period.
“But the reality is that the starting gun has already been fired. The battle is now underway.
“Over the last few weeks, something in Scotland has changed.
“We’ve passed ‘peak Nat’ and, more and more, Scotland is saying ‘enough’.
“An SNP majority government – once seen as a ‘nailed-on’ near-certainty, and for so long the outcome almost universally forecast amongst the pundits – now looks much less sure.
“It’s vital that majority is stopped because it’s the only way to be certain that Scotland isn’t dragged back into another independence referendum when we all need to be focusing on building a recovery from the pandemic.
“At the last election in 2016, the SNP fell just two seats short of an overall majority ... we did it together and we can do it again.”
Ms Davidson is not running for re-election as an MSP and is expected to enter the House of Lords when the current session of the Scottish Parliament ends.
A SNP spokesperson said: "Ruth Davidson has been using that same punch-line for years, hoping it turns out to be true and then realising it isn’t in when the people of Scotland have given their answer in election after election.
"If it was true, perhaps Baroness Davidson wouldn't be running off to the House of Lords to avoid democratic scrutiny."
The Scottish Conservatives virtual spring conference is set to run through to Monday, with Prime Minister Boris Johnson due to speak tomorrow.
Mr Johnson is expected to say he will not allow a second Scottish independence referendum – even if the SNP emerge with a majority from May's Holyrood elections.
The conference comes as the Scottish Tories triumphed in the Leaderdale and Melrose council by-election yesterday, gaining the seat from the SNP.
Tory candidate Jenny Linehan won almost 40 per cent of the first preference votes cast, with the SNP’s John Paton-Day finishing second on 30 per cent.
Scottish Tories leader Douglas Ross said the by-election win showed momentum was with his party ahead of May’s election.