Both Labour leader Jeremy Corbyn and top Liberal Democrat Tim Farron backed the move, while Nicola Sturgeon's SNP abstained.
The election will be held on 8 June, almost a year after the United Kingdom voted to leave the European Union.
Since being fired by Theresa May, Osborne has earned lucrative speaking fees and taken on an advisory role for American investment giant Blackrock.
"The prime minister's attempt to dodge scrutiny shows how she holds the public in contempt", he said. It is actually the "hard" Brexiteers in her own party that are the greatest threat to a successful outcome, with demands that just won't wash with the 27 European Union countries across the negotiating table.
May says politicians should "put our fate in the hands of the people and then let the people decide". It needs support from two-thirds of members of Parliament to pass. Leaders of European Union states are due to adopt negotiating guidelines at an April 29 summit, and the bloc will prepare detailed plans for the talks with Britain by late May.
A European Commission spokesman said the "real political" negotiations on Brexit will start after the election.
But her decision also opens the door to more uncertainty in the region, as it now puts Europe's three most powerful nations - Britain, Germany and France - into full-throttle election mode.
Mr Corbyn retorted: "We welcome the general election but this is a Prime Minister who promised there wouldn't be one, a Prime Minister who can not be trusted".
"This will allow the EU27 to start negotiations", he said. "She says it's about leadership, yet is refusing to defend her record in television debates".
Meanwhile, Mr Corbyn's brother launched a blistering attack on the BBC, saying it will take every opportunity it can to prevent Mr Corbyn becoming prime minister.
"I welcome the news, as a strong majority in Parliament is needed in order to deliver for the country". She said she was confident of reaching a deal in that time frame.
Mrs May could also be ready to ditch promises made in David Cameron's 2015 general election manifesto, such as the commitment to spending 0.7% of national income on foreign aid. "I hope the former will be the case".
Just 12 per cent of Labour voters polled think the party will win a majority on 8 June, according to the poll. He added: "If it isn't a triumphant success, it will be to some extent a personal failure".
Before 2011, a prime minister could dissolve parliament and call a snap election at any time they wanted.
"If the negotiations were coming to a conclusion with a few months to go before a general election our European partners would see that as a sign of weakness and use it to push for concessions".
And justifying her change of mind, she has argued a vote is needed as opposition parties were trying to "frustrate" Brexit.
He said: "I think it is the right thing to do and we need to get on with it".
After addressing a rowdy session of the House of Commons, May won the support of 522 lawmakers in the 650-seat parliament for an election on June 8.