Labour's Val Shawcross has announced that she will stand down from public life in May 2016 when her fourth term of office as London Assembly member for Lambeth and Southwark comes to an end.
A former leader of Croydon Council, Val Shawcross was elected to represent Lambeth & Southwark on the London Assembly when the Greater London Authority was first established in 2000.
She is currently chair of the assembly's transport committee.
In 2010, she was Labour's parliamentary candidate in Bermondsey & Old Southwark.
Before running for elected office, Ms Shawcross worked for the Commonwealth Secretariat and before that for several aid organisations – and now she says that when she leaves City Hall she intends to return to the international development field.
"It has been an absolute honour to serve the people of Lambeth and Southwark and I am very proud of the work my colleagues and I have done at City Hall, holding two Mayors to account and standing up for the interests of our great city and its people," said Val Shawcross in a message to local Labour Party members.
"When I was first elected in 2000 I couldn't have imagined how I would see the Assembly and the Mayoralty develop and the positive impact they would have on London. Whilst there are many memories I will take away with me I am particularly proud of my time spent chairing the London Fire Brigade, modernising the service, introducing a focus on prevention and significantly cutting the number of fire deaths.
"In more recent time in opposition on the Assembly I have focussed on the interests of London's passengers, pedestrians and cyclists and I hope I have helped improve the service they receive from the Mayor and Transport for London. Whilst politics can often be frustrating, particularly in opposition, those who say politics can't make a positive difference are wrong."
Southwark Council leader Peter John said he was "really sorry" to hear of Ms Shawcross's decision to stand down: "She's been a great friend and representative for Lambeth & Southwark," he said.
New Bermondsey & Old Southwark Labour MP Neil Coyle said her departure would ba a "big loss to London".
Green Party London Assembly member Baroness Jones of Moulsecoomb told Ms Shawcross on Twitter: "You have been a wonderful colleague cross party – I wish you success!"
Former Conservative mayoral candidate and Transport for London board member Steve Norris said: "We may not share the same politics but I've always admired Val's commitment and good nature."
Ms Shawcross's decision will now open up a contest in Labour to find a candidate for what is now a safe Labour seat at City Hall.