In a statement released to PRWeek this Wednesday, Windeler said: 'I felt it was time to move to the next stage in my career. I indicated early in 2005 that it was my intention to move on within a year.'
She added: 'I stayed longer than I intended to complete the restructuring of our marcoms offering.'
As to her future plans she said: 'After a short break I intend to develop a portfolio of career interests. I will be sorry to leave H&K, which for over 20 years has been such a central part of my life.'
Laurence wants to pick a replacement before Windeler's exit. Both internal and external candidates are being considered.
Windeler became sole CEO in April 2001, having formerly been joint CEO alongside Laurence. She joined the agency in the mid-1980s when David Wynne-Morgan was CEO.
H&K London is believed to have around 250 staff, down from just under 400 during the industry's boom at the turn of the millennium.
The agency this month lost its pan-European account for Hewlett-Packard (PRWeek, 3 February) but last week picked up major European work for Intel .