The reasons for Ledward's departure are not yet clear and the agency has declined an invitation to comment.
Ledward co-founded Golley Slater's promotional division, alongside associate director Eileen Neale in June 2005.
She joined Golley Slater from the now-defunct Yellow Submarine, where she was a director alongside Neale, and worked on accounts for Channel 4, Canon, COI and Mattel.
Ledward's joining was part of Golley Slater's aim to add promotional business to its portfolio, and she was made managing director of the newly created division when it formed.
Her departure follows that of George Martino, the head of new business and marketing who left the agency last week to take up the same role at RLA Group. He is credited with helping Golley Slater secure its account win for home shopping company Otto UK in February last year.