Labour's Ed Miliband announced his resignation this afternoon saying he took "absolute and total responsibility" for the party's defeat.
Nick Clegg earlier quit as the Liberal Democrat leader after seeing his party annihilated at the polls.
It came as David Cameron went Buckingham Palace to confirm his second term as Prime Minister, at the head of a majority Conservative government.
Mr Clegg said the Lib Dems had suffered a "catastrophic" defeat in the general election, RTE reported.
"Clearly the results have been immeasurably more crushing and unkind than I could ever have feared. For that I must take responsibility and therefore I announce that I will be resigning as leader of the Liberal Democrats."
Earlier this morning, Ukip leader Nigel Farage failed to win Thanet South from the Conservatives.
He lost to Conservative candidate Craig Mackinlay by 2,822 votes.
Afterwards, Mr Farage, who polled 16,026 votes, said he "has never felt happier" with a "weight lifted off his shoulders".
A spokesman for President of the European Commission said that Jean-Claude Juncker had sent his congratulations to Mr Cameron on the election result and looked forward to an early meeting.
However, with attention now turning to the promised referendum on British membership of the EU sometime in the next two years, the spokesman said that the EU's freedom of movement for people, goods, services and capital was not negotiable.