"Since stepping down as prime minister I have enjoyed being a backbencher again and having more time to work for my constituents and champion causes close to my heart including most recently launching a Global Commission on Modern Slavery and Human Trafficking," she said in a statement to her local newspaper, the Maidenhead Advertiser.
"These causes have been taking an increasing amount of my time.
"Because of this, after much careful thought and consideration, I have realised that, looking ahead, I would no longer be able to do my job as an MP in the way I believe is right and my constituents deserve."
May, 67, was first elected as MP for Maidenhead in 1997 and served as home secretary under David Cameron between 2010 and 2016.
She succeeded him as prime minister following his resignation over the result of the Brexit referendum.
Her term in Downing Street lasted a turbulent three years and was dominated by wrangling over Britain's departure from the European Union.Â
A snap election in 2017 resulted in her losing her majority but she remained at No.10 thanks to a deal with Northern Ireland's Democratic Unionist Party in the resulting hung parliament.
Eventually, opposition to her proposed Brexit deal led to Conservative MPs holding a confidence vote in her leadership, and although she survived her authority was diminished and she announced her resignation five months later.
Almost 100 MPs have announced they will not fight their seats at the next election, which is expected later in 2024, including 64 Conservatives and former Conservatives - the most Tories to retire from parliament since May entered the Commons in 1997.
Reuters and PA
