The Brexit Party says it will be contesting 32 of Wales' 40 seats in the general election.
The party has confirmed it will not field candidates in any of the eight seats won by the Conservatives in 2017.
That means they will not be contesting Brecon and Radnorshire, gained by the Liberal Democrats in the 2019 by-election.
Labour claimed the Brexit Party would be a "proxy vote" for the Tories.
Brexit Party leader Nigel Farage announced it would not stand in seats the Conservatives won in 2017.
He said standing in Tory-held seats would have increased the chances of another EU referendum, and would focus instead on taking seats off Labour.
He had previously pledged to field more than 600 election candidates across Britain and on Friday he told BBC Wales the party would contest every Welsh seat.
Nathan Gill, one of the party's MEPs in Wales, told BBC Wales the Prime Minister Boris Johnson had made an important concession by committing to strike a trade deal with the EU without "regulatory alignment".
"We have been very magnanimous," he added. "It has been a very difficult decision but we have unilaterally entered into an alliance".
"We are absolutely confident going into this election in Wales."
This means the Brexit Party will not stand in:
- Brecon and Radnorshire
- Carmarthen West and and South Pembrokeshire
- Clwyd West
- Preseli Pembrokeshire
- Vale of Glamorgan
Aberconwy was won by the Conservatives in 2017, but its former MP Guto Bebb later sat as an independent.
Mark Drakeford AM, Welsh Labour leader and First Minister, said: "If it wasn't clear before, it is now plainly obvious that the Brexit Party is a proxy vote for the Tories.
"They are committed to the same project that will risk jobs through a reckless, damaging Brexit and undermine the very foundations on which our free, universal health service is built. They no more speak for working people than the Tories."
Plaid Cymru leader Adam Price said: "That Nigel Farage is willing to endorse Boris Johnson is proof that they are planning to deliver a disastrous no-deal.
"The fact that he assumes there will be no extension at the end of the next phase is evidence enough that a crash-out Brexit is an inevitability in the eyes of the Brexiteers."
Reacting to the Brexit Party announcement, Boris Johnson said he had "absolutely not" done a deal with Nigel Farage.
"I'm glad that there's a recognition that there is only one way to get Brexit done and that is to vote for us and to vote for the Conservatives," he said.
He added: "We're working very hard for every vote in this election. What we're saying to the country is that we only need nine more seats to get a working majority government."