Mhairi Black secured defeated Douglas Alexander, 47, in Paisley and Renfrewshire South by over 6,000 votes.
Alexander is Labour's foreign affairs spokesman and campaign chief.
The humiliating defeat ends the political career of one of Labour's most senior figures and sums up Labour's dismal performance and an SNP sweep in Scotland.
The SNP bagged 56 of the 59 Scottish seats, the party's biggest election win in history.
Black will be the youngest MP when she takes her seat in the House of Commons later this month after 13-year-old Christopher Monckton who won in 1667.
"The people of Scotland are speaking and it's time for their voice to be heard at Westminster," Black said after her shock victory.
She won cheers from supporters when she pledged the SNP would fight to put an end to austerity cuts that are hurting communities "both north and south of the border".
She managed to turn a 16,614 Labour majority into a 5,684-vote victory thanks to a swing in the vote towards the SNP of 26.9 per cent.
Speaking immediately after the result was declared, Alexander said: "This of course has been a very difficult night for Labour. Scotland has chosen to oppose this Conservative government, but not place that trust in the Labour party. It will be our responsibility to re-win that trust in the months and years ahead.
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