Labour have held Hartlepool since the constituency was created in 1974. Prior to that, 'The Hartlepools' has mostly been held by Labour since the Second World War apart from five years between 1959 and 1964 when it was Conservative.
Yet Mrs Mortimer secured the seat with a comfortable 6,940 majority in the Hartlepool by-election after the town went to the polls on May 6.
So who is the politician behind this historic victory for the Conservatives?
1) Mrs Mortimer lives near Thirsk - around 30 miles from Hartlepool - and is described as a farmer.
2) Before moving to Thirsk, she spent around ten years away from the constituency, living both in London and abroad - including the Cayman Islands in the Caribbean.
3) During her campaign, Labour’s Deputy Leader Angela Rayner challenged Mrs Mortimer over her time in the Cayman Islands, due to its reputation as a tax haven.
However, Conservative co-chairman Amanda Milling slammed Ms Rayner's line of questioning as "factually wrong and entirely disingenuous," as Mrs Mortimer was there due to her then-husband's role in financial services regulation.
Ms Milling clarified that Mrs Mortimer moved to the Cayman Islands with her children due to the job of her ex-husband, "a highly experienced and respected regulator of financial services and a qualified barrister".
The reply noted that Mrs Mortimer’s ex-husband was "a leading authority on financial regulation and has worked and published widely on counter-fraud, anti-corruption, anti-terrorist financing and many other matters".
4) Mrs Mortimer is also a district councillor for the Raskelf and White Horse Ward on Hambleton council in North Yorkshire.
5) She contested the Leeds East seat against Labour in the 2019 General Election but lost by 5,531 votes to sitting MP and former Labour shadow minister Richard Burgon.
6) When campaigning for the Hartlepool seat, Mrs Mortimer listed her priorities as recovering from the pandemic, regenerating high streets and local communities, unlocking the opportunities of Brexit to help create good quality sustainable jobs, helping businesses deliver more apprenticeships, and recruiting more police officers.
She said Labour’s reign over Hartlepool was “why the town has been taken for granted and struggled.”