Former shadow chancellor Ed Balls has lost his seat in the Morley and Outwood constituency in West Yorkshire by 422 votes.
Labour's Mr Balls, who previously had a majority of 1,101 in the constituency on the outskirts of Leeds, lost to the Conservative Andrea Jenkyns.
He polled 18,354 votes but the Conservatives took 18,776, showing a majority of 422 after a tense recount.
Earlier, Respect leader George Galloway lost his seat in Bradford West.
Speaking after being ousted from his seat, Mr Balls said he felt a sense "of sorrow".
He said: "Any personal disappointment I have at this result is nothing compared to the sense of sorrow I have at the result Labour has achieved across the United Kingdom tonight, and the sense of concern I have about the future.
"We will now face five years where questions will arise about the future of our union, about whether we can stay as a member of the European Union and fight for jobs and investment, whether we can make sure we secure our National Health Service at a time when public spending is cut.
"Those are real concerns to me and to many people across the United Kingdom."
Mr Balls' demise spells the end of a decade in Parliament which has seen him at the heart of the Labour machine.
He held the position of chief economic adviser to the Treasury in the Blair government from 1997, working on policies including Sure Start, tax credits and the national minimum wage.
Ed Balls first became an MP in 2005 and a year later was made Economic Secretary to the Treasury.
He was a close adviser to then-chancellor Gordon Brown and earned a reputation as a political bruiser, the Press Association reported.
While the relationship between Mr Miliband and Mr Balls has never been as stormy as that of Mr Blair and Mr Brown, there have appeared to be divisions between the two on Labour's economic policies.
Mr Balls is married to Labour MP Yvette Cooper, who is shadow home secretary, and the couple have three children.
Newly-elected Andrea Jenkyns' website said she left school and went straight into employment as a retail store manager in the constituency at the White Rose Centre and also worked in Guiseley and Wakefield.
She also worked in the public sector as a music tutor in three secondary schools.
Earlier in the morning, the former Bradford West MP Mr Galloway lost out to Labour's Naseem Shah, who won with more than 19,000 votes.
Mr Galloway took the traditional Labour stronghold in a by-election in 2012 with a majority of 10,140 votes.
Earlier, he was reported to police by Bradford Council for allegedly breaking election laws. He is said to have retweeted his party's own exit poll before voting ended.
Ms Shah criticised Mr Galloway's campaign, saying it had "demeaned democracy".
The Labour candidate won with a majority of more than 11,000. Mr Galloway's Respect party won 8,557 votes and the Conservatives 6,160.
Ms Shah is a political newcomer who has overcome childhood poverty, a teenage forced marriage and the imprisonment of her mother for killing an abusive partner.
She had urged voters to reject Mr Galloway, saying: "We do not need a one-man Messiah to tell us how to come and fix up Bradford.''
After being elected, Ms Shah said: "I want to thank the people of Bradford West. You have placed your trust in me to be your voice in Parliament.
"Can I thank all of my opponents - with the exception of one - who all conducted themselves with dignity and fought the election on issues in the spirit of friendly rivalry.
"To Mr Galloway, I say that your campaign demeaned our democracy, but personal attacks on me have not worked.
"The people of Bradford West have seen through this and you have been sent on your way."