John Marek, flanked by Welsh Tory leader Nick Bourne and shadow Welsh secretary Cheryl Gillan. Photo: Conservative Party
John Marek, the former Wrexham Labour MP and AM who left the party because he said it had moved too far to the right, has joined the Conservatives.
The former Welsh assembly deputy presiding officer said Tory leader David Cameron's "social conscience" was behind his decision.
Dr Marek, 69, became an independent after leaving Labour, and then founded a left-wing party, Forward Wales.
Labour reacted by saying he was on a "weird and winding political journey".
Announcing the move in Wrexham, Dr Marek said the Conservatives were the only party who could deliver change.
He became Labour MP for Wrexham in 1983, standing down in 2001 after also being elected the area's Labour AM at the birth of the Welsh assembly in 1999.
Dr Marek, a former applied maths lecturer at Aberystwyth University, said: "David Cameron's social conscience is at the heart of my decision to join the Conservative Party.
"He understands the difficulties faced by ordinary people and I am convinced that as Prime Minister he will govern for everybody.
"I believe it is only through a Conservative government that we can fix our broken economy, restore our civil liberties, ensure our public services meet the public's expectations and tackle the big national and international issues facing our country today."
Nick Bourne, leader of the Welsh Tories, said Dr Marek's decision would bring "strength and experience" to his party.
Mr Bourne said: "I have the greatest respect for John and am extremely pleased he has today joined the Welsh Conservatives.
"His decision speaks volumes for the way in which our party has changed both in Wales and across the UK and has a broad appeal.
"John will add enormous strength and experience to our party. I look forward to working with him in the months and years ahead."
Welsh Labour said: "Since John got himself excluded from the Labour Party seven years ago, we've been watching his weird and winding political journey with increasing disinterest.
"We're unsure whether today's news says more about John or the Welsh Conservatives, but in any case, 'any port in a storm' is the phrase that springs to mind."
As an MP Dr Marek served as a Labour spokesman on Treasury matters.
In the Welsh assembly he gained a reputation as a maverick and in 2001 was elected deputy presiding officer against Labour's preferred candidate, which led to his de-selection as the Labour candidate for the 2003 election.
At that time, Bob Crow, general secretary of the transport union RMT, said it was "an absolute shame that a committed socialist like John has been kicked out".
He then stood as a candidate for the John Marek Independent Party, and was re-elected as an AM, defeating the Labour candidate by 973 votes. Later that year he formed a new political party called Forward Wales (Cymru Ymlaen), which also included another former Labour MP and AM, the ex-Welsh Secretary Ron Davies.
Dr Marek lost his assembly seat to Labour in 2007.
His defection to the Conservatives follows that of former Plaid Cymru AM Mohammad Asghar in December and former Labour AM Alison Halford in 2006.