The Unite to Remain initiative was set up Heidi Allen, prior to her joining the Liberal Democrats, and aims to ensure as many MPs from pro-Remain parties are given a clear run in the upcoming election
As part of this deal, 11 constituencies across Wales will see parties stand aside in order to give each other a clear run. These include all incumbent seats, along with other high profile target seats.
The arrangements mean Plaid Cymru and the Green Party will stand aside for the Welsh Liberal Democrats in Brecon and Radnorshire, Montgomeryshire and Cardiff Central.
Leader of the Welsh Liberal Democrats Jane Dodds said:
"During the by-election in Brecon and Radnorshire, we showed what can be achieved when parties put aside their differences and work together.
"This coming election will decide the fate of our country for generations to come and that’s why the Liberal Democrats have worked with the Green Party and Plaid Cymru to put the national interest first.
"This historic cross-party initiative gives us the best chance to return more MPs from Remain parties to further the fight to stop Brexit and I would like to thank Plaid Cymru and the Greens for taking part in these talks.
"But while the Liberal Democrats have been leading, Labour has been sitting on the sidelines. They did not take part in the talks and now risk splitting the vote in a number of key marginal constituencies across the UK.
"So, on December 12th, if you want to stop Brexit, vote for the Liberal Democrats or your Unite To Remain