The voters will elect the 56th Parliament of the United Kingdom after the Fixed-term Parliaments Act 2011 led to the mandated dissolution of the 55th Parliament on March 30, 2015.
There are also local elections scheduled to take place on the same day across most of England, with the exception of Greater London.
Polls open at 07:00 BST on Thursday, May 7, at around 50,000 polling stations across the UK.
A total of 650 Westminster Members of Parliament (MPs) will be elected for the House of Commons, the lower house of Parliament, with about 50 million people registered to vote.
As well as the general election, there are more than 9,000 council seats being contested across 279 English local authorities.
Mayors will also be elected in Bedford, Copeland, Leicester, Mansfield, Middlesbrough and Torbay.
This means that nearly every voter in England – excluding London where there are no local elections – will be given at least two ballot papers when they enter polling stations.
Some votes have already been cast, through postal voting, which accounted for 15% of the total electorate at the 2010 general election, when the overall turnout was 65%.
For the first time, people have been able to register to vote online.
Most polling stations are in schools, community centres and parish halls, but pubs, a launderette and a school bus will also be used.
A handful of seats are expected to be declared by midnight, with the final results expected on Friday afternoon, May 8.
Polls close at 22:00 BST, but officials say anyone in a polling station queue at this time should be able to cast their vote.
Seven parties (Conservative, Labour, Liberal Democrat, UKIP, SNP, PC and Green) participated in the election leadership debates.
The Conservative Party and Labour Party have been the two biggest parties since 1922, and have supplied all UK prime ministers since that date. Polls predict that these parties will receive between 65-75% of the votes and win 80-85% of seats between them and that as such the leader of one of these parities will be the prime minister after the election.
The Economist described a “familiar two-and-a-half-party system” (Conservatives, Labour, and the Liberal Democrats) that “appears to be breaking down” with the rise of the United Kingdom Independence Party (UKIP), the Greens and the Scottish National Party (SNP).
Analysts say that there will be no overall majority, but that PM David Cameron’s Conservatives will be the largest party with more than 280 seats.
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