The 57-year-old’s decision also ends a long association with West Ham co-owner David Sullivan which dates back to when she persuaded him and the late David Gold to buy Birmingham City in 1993.
Aged just 23 at the time, she became managing director of the club in a revolutionary moment for a male-dominated sport.
Brady left Birmingham in 2009 when Sullivan and Gold sold the club – but a year later they were together again at West Ham.
Perhaps the most significant singular achievement by Brady off the pitch during her time at the Hammers was playing a leading role in them leasing the London Stadium.
It had hosted the athletics and the opening and closing ceremonies at the 2012 Olympics.
Securing the stadium helped propel West Ham into the top 20 wealthiest clubs in the world, according to Deloitte.
On the pitch they have been in the Premier League since the 2012/13 campaign and won the Europa Conference League in 2023, their first major trophy since the 1980 FA Cup.
“It has been a privilege to work alongside the board, management, players, staff and supporters at West Ham United,” she said in a statement sent to The Times.
“Together we have achieved remarkable milestones, but the highlight for me will always be lifting the Uefa Europa Conference League trophy – a moment that will stay with me forever.”
However, Brady, who was ennobled and whose profile grew with her aiding former Spurs owner Alan Sugar in the BBC television hit “The Apprentice,” also attracted a lot of abuse as she highlighted in 2019.
“Curses have been spat at me, abuse sung and chanted at me – by phone, on paper, and latterly in social media,” she wrote.
“Truly, knowing what I know now, I don’t think I would have bothered.”
Nevertheless she soldiered on and in her valedictory statement on Tuesday suggested football had not yet seen the last of her.
“While this chapter closes, my passion for football and commitment to supporting the next generation of leaders remains undiminished,” she said.
“I wish West Ham United every success for the future and look forward to following their continued achievements with pride.”
She leaves with West Ham’s Premier League status in the balance.
They are just two points above third-from-bottom Tottenham Hotspur with five matches remaining. (AFP)