On 16 July 2015, Brown became Interim Commissioner of Transport for London after the departure of Sir Peter Hendy.
[5] Following the November 2016 Croydon tram derailment, he was one of two top Transport for London (TfL) officials to decline a performance bonus.
[8][9] In October 2019, TfL announced that Brown would be leaving his role as Commissioner in May 2020 to chair the Delivery Authority for the restoration of the Houses of Parliament.
[11] Brown was appointed Member of the Royal Victorian Order (MVO) in the 2002 Birthday Honours[12] "for services to the Golden Jubilee" for his work at TfL during what has been called "one of the Underground’s greatest-ever organisational challenges".
[13] In 2020, he was appointed Commander of the Order of the British Empire (CBE) in the 2020 Birthday Honours for services to transport.