She said: "Mr Melville believes it is important to support officers in expressing their legitimate views. He regularly attends events… to show support for his officers… and he is proud to do so with this march as well."
Paul McKeever, chairman of the Police Federation, said many other chiefs had privately expressed support, although none had publicly declared that they would be attending the event.
The march will see rank-and-file officers carry banners declaring that the cuts are "criminal" as they march past the Home Office and down Whitehall.
Some are demanding the right to strike - to which police are currently not entitled. Demonstrators will have to take a day off to march.
Mr McKeever said officers were driven to act by a "volatile mix" of reforms and cuts imposed by the Government.
He said they included 20% cuts to force budgets, reductions in police pay, changes to working conditions, creeping privatisation of the service, cuts to numbers of frontline officers of more than 5,000 in the last year alone, and the politicisation of policing with the election of commissioners.