John Bercow pledged to heal public “anger and disappointment” over the expenses scandal as he was installed as the UK's House of Commons’ 157th Speaker.
The Buckingham MP completed a remarkable political journey from right-wing firebrand to pillar of the establishment by claiming parliament’s top job.
Gordon Brown praised his “leadership and integrity”, while David Cameron said he “wished him well”.
But there were immediate questions over whether Mr Bercow would have the authority to carry through crucial reforms, as relatively few of his Tory colleagues are thought to have backed him, and many were vehemently opposed.
Mr Bercow’s moment of triumph came after a marathon six-hour selection process, culminating in a series of secret ballots.
He secured the most votes in the first two rounds, as eight other candidates, including former Cabinet minister Margaret Beckett, were either eliminated or dropped out. A dramatic head-to-head with fellow Conservative Sir George Young ensued, with Mr Bercow supported by 322 MPs compared to 271 for his opponent.
After being “dragged” to the chair in a traditional Commons ritual, he told the House: “I thank you from the bottom of my heart for the confidence that you have placed in me and I am keenly aware of the obligations into which I now enter.
“My commitment to this house is to be completely impartial between members of one political party and another.”
He went on: “We have faced quite the most testing time which has left many members feeling very sore and vulnerable but large sections of the public also feel angry and disappointed.
“I continue to believe the vast majority of Members of this House are upright, decent, honourable people who have come into politics not to feather their nests but because they have heeded the call of public service.
“For such people I shall always have the highest respect and it is on that basis, in that spirit, and with that conviction, that I shall seek to discharge my obligations in this House which I regard, as I have said, as the greatest privilege of my professional life to occupy.”
For Mr Bercow to have been elected as Speaker in a Labour-dominated chamber, and seemingly against the wishes of most Tory MPs, was one of the stranger quirks of politics.
In his youth he was a leading member of the Conservative Party’s right-wing Monday Club, which was notorious for a hard-line stance on immigration and its “Hang Nelson Mandela” slogan.
Even the manager of his Speakership campaign, Reading MP Martin Salter, admits that he would have once “knocked his block off” for his extreme views.
But over recent years Mr Bercow’s politics has shifted substantially to the social liberal Left, a change that many have attributed to the influence of his Labour-supporting wife.
There have been persistent rumours that he could “cross the floor”, and he infuriated his own party further two years ago by accepting an advisory role on children’s speech problems for Mr Brown.
He was enthusiastically applauded by the Labour benches last night, but the Opposition ranks remained muted.
As few as 30 Conservatives are estimated to have supported Mr Bercow’s candidacy. Some, including Mid Beds MP Nadine Dorries, have insisted he is effectively Labour’s third Speaker in a row, and pledged to try and replace him after the next general election.
Doubts were also raised because of his relative youth at 46, and criticism of his expenses. He was accused of “flipping” home designation to maximise claims, and using public money to pay for accountants to do his tax return.
Mr Bercow was formally confirmed in his role in a ceremony in the House of Lords, where he received Royal approval.
Welcoming his appointment, Mr Brown said: “Today we have an opportunity to start a new chapter with a new Speaker.”
David Cameron offered his congratulations, but warned: “We share a collective responsibility for what went wrong, we share a collective responsibility for putting it right.”
Lib Dem leader Nick Clegg urged Mr Bercow to get on with the job of change, telling him: “You have a mandate for change, not just from the votes you won today, but from the people of Britain.”
Mr Bercow will get an immediate pay hike to £141,866 a year. Unless the rules are changed, on standing down he will also get the ultra gold-plated pension given to all former Speakers – equivalent to £40,000 a year index-linked, in addition to his generous MP pension.
Tomorrow the new Speaker is expected to talk to the media as he bids to restore the Commons’ reputation in the wake of the expenses row that forced out his predecessor, Michael Martin.