At 27 Ms Smith now becomes the youngest MP at Westminster (move over Jo Swinson) when parliament returns in September.
A lowish turnout, 45%, gave the Tories a stonking 13,591 votes and a majority of 7348. The 16.49% swing is almost as good as Crewe and Natwich, last year's by election where the Conservatives had a swing of over 17%. Stunning result which just adds to the humiliation of Gordon Brown's premiership.
Ms Smith had more than twice as many votes as the Labour candidate Chris Ostrowski, who retreated from the field a few days ago suffering with swine flu. He had 6,243 votes but no one can blame him.
The Lib Dems came third with 4,803, narrowly ahead of UKIP on 4,068 and the Greens were a low 3350 despite the hype that they would benefit from the local disgust with how former MP Ian Gibson was treated.
He resigned when the party's star chamber ruled that he could not stand again because he claimed expenses to pay for his London mortgage, as many MPs do, but then sold the flat at a reduced rate to his daughter (Was he meant to over-charge her?)
David Cameron will be up in Norwich for a victory lap this afternoon He'll know his way around by now - he's had to be there six times to secure this victory and he can't be in every one of the 120 seats the Tories have to win for an overall majority in Westminster. But this looks good for team Cameron.
For Labour it is bad, but not that that bad, on the gloom scale that the party finds itself in even though the Tories say it is the lowest share of the vote by any governing party in a by-election for 40 years.
In a campaign that was blighted not just by disgruntlement with Gordon Brown and anger over the expenses scandal and plain disgust over how Ian Gibson was "scapegoated" they could have only expected a drubbing.
Cameron press conference in Norwich due at 3pm. Words from the PM imminent.