Labour has taken Stockton South from the Conservatives by just 888 votes.
Paul Williams, a local GP who has spent most of his career in the North East, took the seat from James Wharton in a shock election result.
Stockton South is regarded as one of those seats that a party has to win, if it is to form a government.
Speaking to ITV Tyne Tees Mr Wharton said we live in a "strange time politically" with Labour "promising everyone everything and promised someone else will pay for it."
But he said he didn't dismiss the shock result and said there are lessons to be learned.
He added: "I hope those lessons are learned, but I do worry that,0 at a crucial time for our country as we negotiate Brexit and chart our new course in the world, this sort of instability will not help but hinder our prospects."
Former ITV Tyne Tees political correspondent Paul Brand called the defeat of James Wharton "unbelievable" while ITV News political editor Robert Peston said on twitter it was the most significant result of the night.
James Wharton held the seat for the Conservatives from 2010, winning it back from Labour with a slender majority of just 332. He backed Brexit and increased his majority in 2015 to just over 5,000, and was appointed Northern Powerhouse Minister until 2016.
Stockton South was previously held by the Conservatives from 1987 to 1997 and before that, by Ian Wrigglesworth for the SDP.
Former chancellor George Osborne said Wharton was not someone "we should be losing from parliament" adding: "there will be a very big post-mortem coming."