The Lib Dems, Plaid Cymru and the Green Party have agreed to not run candidates against each other in 60 seats across England and Wales, in an attempt to get more pro-Remain MPs elected on December 12.
Under the plan revealed on Thursday, the Lib Dems will be given a free run in 43 seats, the Greens will be unopposed in 10 and Plaid Cymru have been handed seven.
Labour is not taking part in the pact.
The deal, brokered by the Unite To Remain group, follows an agreement earlier this year in the Brecon and Radnorshire by-election, where the Lib Dems took the seat from the Conservatives after the other two parties stood aside.
Jo Swinson, the Lib Dem leader, said she was “delighted” that an agreement has been reached.
Adam Price, leader of Plaid Cymru, said: “In these deeply serious times we need grown-up politics that puts our countries before parties.”
Sian Berry, co-leader of the Green Party, said: “The crash-out Brexit the Tories are pushing for would be a disaster for people up and down England and Wales. And for action on climate chaos.”
The Lib Dems have also decided to stand down in Beaconsfield to help former Tory MP Dominic Grieve and in Broxtowe and in Luton South to help Change UK’s Anna Soubry and Gavin Shuker.
Remain-alliance seat list in full
Green Party (10)
Brighton Pavilion
Isle of Wight
Bristol West
Bury St Edmunds
Stroud
Dulwich and West Norwood
Forest of Dean
Cannock Chase, Exeter
Vale of Glamorgan
Liberal Democrats (43)
Bath
Bermondsey and Old Southwark
Brecon and Radnorshire
Buckingham
Cardiff Central
Cheadle
Chelmsford, Chelsea and Fulham
Cheltenham
Chippenham
Esher and Walton
Finchley and Golders Green
Guildford
Harrogate and Knaresborough
Hazel Grove
Hitchin and Harpenden
Montgomeryshire
North Cornwall
North Norfolk
Oxford West and Abingdon
Penistone and Stocksbridge
Portsmouth South
Richmond Park
Romsey and Southampton
North Rushcliffe
South Cambridgeshire
South East Cambridgeshire
South West Surrey, Southport
Taunton Deane
Thornbury and Yate
Totnes
Tunbridge Wells
Twickenham
Wantage
Warrington South
Watford
Wells
Westmorland and Lonsdale
Wimbledon
Winchester
Witney
York
Plaid Cymru (7)
Arfon
Caerphilly
Carmarthen East and Dinefwr Dwyfor
Meirionnydd,
Llanelli
Pontypridd
Ynys Môn