Nigel Farage will visit south Wales later “to kick things off” for the Brexit Party’s general election campaign.
The party is targeting “Labour heartland seats”, says MEP Nathan Gill.
Mr Gill said people in the south Wales valleys “will never vote Tory but they will vote for the Brexit Party”.
Mr Farage told BBC Radio Wales the party had 40 candidates ready to contest every seat in Wales.
“Clearly our real focus is many of those Labour-held seats that voted very strongly for leave that are now represented effectively by remain MPs who want to force a second referendum on them.”
Mr Farage added Prime Minister Boris Johnson’s deal was “not Brexit”.
He said: “We’ve been through three years of agony, Boris’ so-called deal gives us another three years of agony and I think when people realise that, they’re pretty upset.
“I’m urging the prime minister, stand up and say that you will change this deal further still so that it really starts to look like Brexit.”
Following a pact between the pro-remain parties Liberal Democrats, Plaid Cymru and the Green Party not to stand against each other, Mr Farage said he had believed a “leave alliance” would be a “good idea, but apparently that’s not wanted”.
Mr Gill also told BBC Wales Mr Johnson’s Brexit deal was almost exactly the same as the one his predecessor Theresa May had negotiated with EU leaders.
Mr Gill said the prime minister had voted twice against Mrs May’s deal and Mr Johnson had called that agreement “vassalage”.
“All the things we said we’d be able to do, we won’t be able to do, it’s not Brexit, it’s not taking back control,” he said.
“Millions of people voted for taking back control but under the prime minister’s deal we’re giving too much control still to the EU and Brexiteers don’t like it.”
Mr Gill, who is one of two Brexit Party MEPs in Wales, defended the decision of party leader Mr Farage not to stand in the election.
“It’s a sign of pragmatism,” he said.
“It’s much better for Nigel to be fighting the air war for us, doing all the media, coming to Wales and making sure we get Brexiteers elected so we can have a great deal of effect when there’s a hung parliament on 13 December.”
He added: “We’re targeting those Labour heartland seats in the south Wales valleys which have been left behind for years and years.
“They will never vote Tory but they will vote for the Brexit Party. They are all Brexiteer seats.”
The party has never had an MP in Wales.
It has four Welsh Assembly members.
Like Mr Gill, they were previously members of UKIP, the party Mr Farage used to lead.