Rosie Cooper has formally stood down as Labour MP for West Lancashire sparking a Red Wall by-election.
She was previously the target of a murder plot and admitted "events I have faced have taken their toll".
Far-right extremist Jack Renshaw was handed a life sentence for plotting to murder the MP in 2019.
His attempt was foiled by whistleblower Robbie Mullen, who was at a meeting in a pub when Renshaw announced he was going to kill Ms Cooper in July 2017.
She has been appointed Steward and Bailiff of the Three Hundreds of Chiltern by the Chancellor, the archaic process that effectively resigns an MP.
She previously said she had accepted the position of chair of Mersey Care NHS Foundation Trust "after a considerable period of soul-searching and reflection".
This appointment meant she was unable to continue with her duties as an MP, she said.
Ms Cooper, who has held the seat for 17 years, has a current majority of just over 8,300.
Her resignation will mean a by-election in a constituency firmly in the "Red Wall" which Sir Keir Starmer will be looking to hold.
A statement from the Treasury said: "The Chancellor of the Exchequer has this day appointed Rosemary Elizabeth Cooper to be Steward and Bailiff of the Three Hundreds of Chiltern."
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