The Gardens & Parks Panel provides an external reference point for the trust and advises on issues relating to the plant collections, the conservation of gardens and parks, and the management and interpretation of those open to the public.
St. Modwen, the UK’s regeneration specialist and owner of Trentham Estate and Gardens, is allowing Walker the time to dedicate to his role at the National Trust, seeing it as an extension of his work.
Walker said: "My appointment as chairman of the Garden & Parks Panel is a great honour, and one I could not possibly have envisaged when I first joined the National Trust way back in 1981.
"The trust is responsible for the largest collection of gardens and parks under single ownership in Europe, if not the world, so it is an extremely exciting organisation to be part of."
Mike Calnan, head of gardens at the National Trust, said the appointment was a tribute to walker's standing as one of the top horticulturalists in the UK and to his knowledge of historic garden management.
"He brings a wealth of experience, combined with exceptional advisory and leadership qualities which will benefit trust gardens enormously. We are greatly looking forward to working with Michael in his new role."