The former leader of the Brexit Party group in the Welsh Parliament has joined the Abolish the Assembly Party.
Mark Reckless said the Brexit Party had achieved its goal in seeing the UK leaving the EU.
He said he was joining the Abolish the Assembly Party "to help give those opposed to devolution a proper voice".
The Brexit Party no longer has any members of the Senedd (MSs) after David Rowlands and Mandy Jones created the Independent Alliance for Reform group.
They will be joined by Caroline Jones, herself a former Brexit Party MS who left the group earlier in the year.
In a statement, Mr Reckless, a former Conservative MP who defected to UKIP in 2014, said: "The Brexit Party has achieved its goal now that we are properly leaving the European Union."
The South Wales East MS said he was "joining the Abolish The Assembly Party to help give those opposed to devolution a proper voice in Welsh politics".
"Devolution has until now only ever been one way, with more and more powers devolved. Now they are even enforcing a border with England [with the Covid travel ban].
"Next year we could see income tax rise just in Wales under new powers."
On Friday, his former Brexit Party colleagues David Rowlands and Mandy Jones joined the independent member Caroline Jones to form a new political group in the Senedd, the Independent Alliance for Reform.
The new group will be the fourth-largest in the 60-member Senedd, or Welsh Parliament, which changed its name from the National Assembly for Wales in May, and they say they will focus on reforming devolution, rather than abolition.
In becoming a member of the Abolish the Assembly Party, Mr Reckless joins another former UKIP MS, Gareth Bennett.
The Brexit Party Senedd group, formed by ex-members of UKIP including Mr Reckless and backed by former UKIP leader Nigel Farage, came together in 2019.
Mr Reckless was originally elected as a UKIP assembly member in 2017, before later joining the Conservatives in the chamber.
Of the original UKIP group only Neil Hamilton, now the party's interim UK leader, remains.
Michelle Brown, a former UKIP member who now sits as an independent, said she did not expect to join either the new group or the abolition party.
A third member would allow the abolition party to form a Senedd group and attract extra funding for staff.
"If we want to cure our country's ills, it's the party in government that needs changing, not the Welsh Parliament itself," Ms Brown said.
"As far as me joining 'Reform' or 'Abolish the Assembly' is concerned, I'd rather dive into a pool of my own vomit than join either of them," she added.