The wife of former Sheffield MP Harry Harpham said today she would carry on the work her late husband started in Westminster after being elected today.
The former Labour councillor won by nearly 10,000 votes.
Ms Furniss paid tribute to the people of Sheffield and denounced the current Tory government.
She said: “The people of Brightside and Hillsborough have sent David Cameron an emphatic message. We’ve had enough of your uncaring government.
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“We’ve had enough of these unfair cuts which have hit communities like ours in Sheffield so much more than affluent areas.
Ms Furniss paid tribute to her late husband who lost his battle with cancer in February.
“This is a by-election none of us wanted. My husband Harry was a fantastic MP for his constituency.
“He was also a loving husband, father and we all miss him a great deal.
“He would’ve wanted me to stand in this election to carry on his work both here in Sheffield and in Westminster.”
Labour’s deputy leader Tom Watson was in Sheffield to show support to the newly elected MP.
He said: “We’ve had a brilliant campaign in Gill Furniss she’s a brilliant campaigner.
“She’s worked her socks off in this by-election and she’ll be a powerful voice for Sheffield in Westminster.
But Mr Watson said today’s result did come with a hint of sadness.
“For everyone in the Labour family for us it’s quite a sad evening. Harry was a friend of mine and we remember him with great affection.
“I felt very proud for him to be the last MP miner to be elected to Westminster and that really means something in the Labour party. He was a great man.”
In what was a low turnout of 33.2 per cent, Ms Furniss pledged to fight for her constituents down in Westminster.