Speaking outside Downing Street on Tuesday in an unexpected announcement, May said that during a time of enormous national significance there should be unity in Westminster, but there is instead division.
In her speech, May said: "Last summer, after the country voted to leave the European Union, Britain needed certainty, stability and strong leadership, and since I became Prime Minister the government has delivered precisely that.
"Despite predictions of immediate financial and economic danger, since the referendum we have seen consumer confidence remain high, record numbers of jobs, and economic growth that has exceeded all expectations. We have also delivered on the mandate that we were handed by the referendum result.
"Britain is leaving the EU and there can be no turning back. And as we look to the future, the government has the right plan for negotiating our new relationship with Europe. We want a deep and special partnership between a strong and successful EU and a UK that is free to chart its own way in the world.
"That means we will regain control of our own money, our own laws and our own borders and we will be free to strike trade deals with old friends and new partners all around the world.
"This is the right approach, and it is in the national interest. But the other political parties oppose it. At this moment of enormous national significance there should be unity here in Westminster, but instead there is division. The country is coming together, but Westminster is not.
"Division in Westminster will risk our ability to make a success of Brexit and it will cause damaging uncertainty and instability to the country. So we need a General Election and we need one now."
May has been Prime Minister since July 2016 after her predecessor David Cameron resigned. The Prime Minister can call an election if two-thirds of lawmakers vote for it under Britain’s Fixed-Term Parliaments Act.
Terry Scuoler, chief executive of EEF, the manufacturers’ organisation, said: “Industry will welcome the Prime Minister’s decision to seek a clear mandate. The last year has been one of considerable uncertainty which, if it had gone on unchecked, would have risked hampering future investment.
“We have significant negotiations to undertake with our partners in the rest of Europe and, doing this with a fresh and stable mandate from the country can only provide greater certainty about the future direction of travel for policy, and the potential to seek the best deal possible for the UK.”
Carolyn Fairbairn, CBI director-general, said: “With a snap General Election now called, businesses will be looking to each political party set out their plans to support economic stability and prosperity over the next Parliament in a way that is fair and sustainable for communities across the UK.
“Distraction from the urgent priorities of seeking the best EU deal and improving UK productivity must be kept to a minimum. Firms will want to hear commitments from all parties to work in close partnership with business and back a new Industrial Strategy to make the UK economy the most competitive in the world by 2030.
“It is essential to get the UK’s foundations right, from building a skills base for the next generation, to investing in infrastructure, energy and delivering a pro-enterprise tax environment.
“As EU negotiations now get underway, firms are clear about the serious risks of failing to secure a deal and falling into World Trade Organisation rules. It is vital that negotiators secure some early wins and all parties should commit to working to ensure businesses can continue to trade easily with our EU neighbours, while seeking new opportunities around the world.
“Whoever forms the next government, they should seek to build a partnership between business and government that is the best in the world, based on trust and shared interest.”
Labour leader Jeremy Corbyn said: “I welcome the Prime Minister’s decision to give the British people the chance to vote for a government that will put the interests of the majority first.
“Labour will be offering the country an effective alternative to a government that has failed to rebuild the economy, delivered falling living standards and damaging cuts to our schools and NHS.
“In the last couple of weeks, Labour has set out policies that offer a clear and credible choice for the country. We look forward to showing how Labour will stand up for the people of Britain."
Tim Farron, Liberal Democrat leader, said: “This election is your chance to change the direction of our country.
“If you want to avoid a disastrous Hard Brexit. If you want to keep Britain in the Single Market. If you want a Britain that is open, tolerant and united, this is your chance.
“Only the Liberal Democrats can prevent a Conservative majority.”
MPs have since voted 522 to 13 in favour of an early General Election.