In a candid admission, Wyllie said she had resigned because she did not have the right skills to take the agency forward.
Headhunters have been called in to help search for a UK CEO replacement for Wyllie, who is also Porter Novelli president for EMEA. Wyllie will stay on until a replacement has been appointed.
'It has been a joy to work at Porter Novelli and there is immense talent at the agency,' said Wyllie.
'But the company needs someone with a different skills set than me to take it forward. It needs someone else to take it to the next level.'