The Green Party's Caroline Lucas has held her seat in Brighton Pavilion with an increased share of the vote.
Ms Lucas, who became the party's first MP in 2010, gained 22,871 votes, ahead of Labour's Purna Sen with 14,904.
She said the election campaign was the "most successful" ever for the Greens.
However, despite a record vote share of 3.8%, the party did not add to its one seat, missing out in key targets Bristol West and Norwich South.
The swing of 10.1% to the Greens in Brighton Pavilion came largely at the expense of the Liberal Democrats, who were down 11% on 2010 with 1,525 votes, finishing fifth.
The Conservatives were in third place and UKIP fourth.
Following her win, Ms Lucas said the Greens had "made history" and had had the "most successful election campaign ever, with almost a million people voting Green".
However, she added that the results had shown "the political system in this country is broken".
"It's ever clearer tonight that the time for electoral reform is long overdue, and it's only proportional representation that will deliver a Parliament that is truly legitimate and better reflects the people it is meant to represent."
Green Party membership has surged in recent months and the party had hoped it would translate into more parliamentary seats.
Green Party leader Natalie Bennett finished third in the safe Labour sweat in Holborn and St Pancras.
Analysis, by BBC correspondent June Kelly
Natalie Bennett was one of the fresh faces of this election. Following in the trail of Caroline Lucas, an assured leader and media performer, was always going to be tough.
Ms Bennett came a cropper before the campaign had begun with a shambolic radio interview which she put down to "brain fade".
After that, her personal challenge was to demonstrate she was a competent leader with a grip on policy.
She stood in the central London seat of Holborn and St Pancras. This was safe Labour territory and she came third, ahead of the Lib Dems.
Like other leaders of the smaller parties, Ms Bennett was given a more public platform in this ground breaking election.
We were told voters were hungry for alternatives. The Green leader needed to capitalise on this and broaden the party's appeal. It appears they have increased their share of the vote, including in some of the big northern cities.
Put to her that there had been no Green "surge", Ms Bennett pointed to increases in the party's membership.
And she restated her pledge that the party would do "everything we possibly can" to ensure there was not a Conservative government.
Asked whether she would step down if the party did not perform well, Ms Bennett replied: "I'll be serving out my full two years' term."