Mrs Mortimer was declared the winner at just after 7am on Friday morning with a majority of 6,940 votes.
She received 15,529 votes with Labour’s Paul Williams finishing second on 8,589 votes and independent challenger Samantha Lee coming third with 2,904 votes.
Mrs Mortimer successfully overcame a 3,595 majority held by former Labour MP Mike Hill after his sudden resignation triggered the by-election.
The 56-year-old farmer and North Yorkshire district councillor is the first Conservative MP to serve the town since naval hero Commander John Kerans stood down ahead of the 1964 General Election.
After her triumph was confirmed, she said: “I’m incredibly proud of the campaign my team and I have run in Hartlepool.
"It’s been based on the local issues of real concern to the community her and I would like to thank all the people of this town who have responded so positively to it.
"I’m also immensely proud to be the first Conservative MP in Hartlepool for 57 years. Not only that I’m the first woman to be elected as MP for this town.
"It’s a truly historic result and a momentous day.”
Mrs Mortimer campaigned on having a plan for jobs through the new freeport, apprenticeships, regenerating the town centre and cutting crime with more police on the beat.
Her election bid was boosted by three visits to Hartlepool by Prime Minister Boris Johnson and a number of other senior ministers.
It also appears to have benefited from the Government’s Covid vaccine programme.
With counting delayed as votes for four separate elections needed to be firstly verified, it was daylight before her victory was confirmed.
The long evening had been punctuated by the mystery appearance outside the Mill House Leisure Centre count of a giant inflatable of Prime Minister Boris Johnson.
The real thing is expected to travel north once again to Hartlepool at some point over the weekend to congratulate the new MP.
Her victory, however, is a blow to Labour leader Sir Keir Starmer, who also visited Hartlepool three times, in what was seen as his first major political challenge since replacing Jeremy Corbyn.
The full by-election result was:
Jill Mortimer (Conservative Party) 15,529
Paul Daniel Williams (Labour Party) 8,589
Sam Lee (Independent) 2,904
Claire Martin (Heritage Party) 468
John Prescott (Reform UK) 368
Rachel Sara Featherstone (The Green Party) 358
Andrew Michael Hagon (Liberal Democrat) 349
Thelma Doris Walker (Northern Independence Party) 250
Chris Killick (Independent) 248
Hilton Dawson (The North East Party) 163
W. Ralph Ward-Jackson (Independent) 157
Gemma Evans (Women's Equality Party) 140
Adam Gaines (Independent) 126
Nick “The Incredible Flying Brick” Delves (The Official Monster Raving Loony Party) 108
David Bettney (Social Democratic Party) 104
Steve Jack (Freedom Alliance) 72