Donald Brydon has announced he will step down as chairman of Royal Mail after six years at the postal service.
Having overseen the one of the most significant periods in the Royal Mail's history, Brydon said the time was right to step down.
Brydon helped lead the controversial privatisation of the UK's postal service in 2013.
Royal Mail chief exec Moya Greene, herself the subject of departure speculation, said: "Donald has played a key role as chairman during one of the most eventful periods in our history. I would like to personally thank him for his support and counsel."
The search for a successor will begin and the firm expects Brydon to remain chair until at least the summer, when it holds its annual general meeting.
Brydon, who is also chair of software firm Sage, said: "I am proud of what Royal Mail has achieved as a company in the last six years. Our transformation is well underway and we are now a FTSE 100 listed company. I feel that now is the right time for me to make this decision."
Brydon's exit comes as the company faces increasing competition from rival parcel delivery firms, including Amazon, which has launched its own delivery network.