Noble made a sudden exit from the WPP firm this week, without a new role lined up.
New York-based global CEO Donna Imperato is understood to have flown in to London to hold crunch talks with the former Freuds director on Tuesday.
WPP sources said these talks ended with Noble leaving the building.
Noble is being replaced by Weber Shandwick corporate MD Scott Wilson, who was offered the role two weeks ago and is now on gardening leave from WS.
Imperato said Noble was leaving by mutual agreement, declaring the move 'the final part of our restructuring'. She added: 'Fiona has been a very valuable colleague. We're now at point where we need to take a different road ahead.'
However, Noble insisted that she had resigned. She said: 'I've done two years - coming to a brand that needed some real restarting. We've got good people and there are some things that I'd like to now go and do. I came in with a specific brief, now I am ready to do something new.'
Wilson will join C&W in the next three to six months. In the meantime, the London agency will be run jointly by global head of healthcare Mike Kan and global head of corporate Geoff Beattie.
At Weber Shandwick, Sainsbury's head of consumer PR Rachel Friend replaces Wilson.
Friend will join the agency in mid-August, having worked at Sainsbury's since 2008. Previously, she was at Hill & Knowlton.
Weber Shandwick European CEO Colin Byrne said 'The appointment is designed to bring in new blood at the most senior level and deepen our domestic PR business in consumer. We could do better on our domestic client base.'
The major players
Fiona Noble - Former Freud Communications MD took the top role at Cohn & Wolfe in 2008
Donna Imperato - Global CEO of Cohn & Wolfe since 2002. She has been with Cohn & Wolfe since 1997
Scott Wilson - Former journalist was appointed MD of Weber Shandwick's consumer division in 2005. He headed a 40-strong team at Shandwick