A PACT between the Liberal Democrats, Plaid Cymru and the Green Party that helped Jane Dodds win the Brecon and Radnorshire by-election will be repeated. It is significant because it could prove to be a decisive factor in marginal seats where Remain voters could split their vote between different candidates, and because previous cross-party attempts to co-ordinate Remain pacts have failed.
The election begins five weeks on Thursday, on December 12.
The Conservatives are now on course to win the election, with a YouGov poll conducted earlier this week placing the Conservatives on 38%, Labour on 25%, the Liberal Democrats on 16%, and the Brexit Party on 11%.
The Lib Dems says they are putting the national interest above party politics to deliver Remain.
Adam Price, leader of Plaid Cymru, said: "In these deeply serious times, we need grown-up politics that puts our countries before parties".
It is understood an announcement on the deal impacting on more of a quarter of the seats in Wales will be announced in central London today.
But one Welsh seat which is not included in the deal is Ceredigion, where the Tories trailed in fourth place in 2017.
The deal does not involve the Ceredigion seat - now held by Plaid Cymru but a top election target for the Lib Dems who are also expected to have a free run at the Brecon and Radnorshire seat, won by in the August by-election.
Candidates will stand aside for each other in 11 of the 40 seats in Wales in order to increase the chances of a remain-supporting MP being elected.
It will give the Liberal Democrats a clear run in both constituencies in what is described by the party's leader Jo Swinson a "numbers game".
Labour is also having nothing to do with the Remain pact because it believes it could hurt it in Labour-leaning constituencies which voted to Leave in 2016.
Prime Minister Boris Johnson last week during the election after Nigel Farage called on him to drop his new Brexit deal with the European Union in a "Leave alliance".
The project, called Unite to Remain, and led by the former MP Heidi Allen, has been launched more widely after they claimed initial success in the Brecon and Radnorshire byelection earlier this year. "We will never enter pacts, coalitions, or deals like that - ever".