Speculation that Nides might depart began last month after John Mack unexpectedly returned as CEO at Morgan Stanley. Nides and Mack have worked together at several different financial companies, most recently Credit Suisse First Boston in 2004.
Nides called the decision to leave 'excruciatingly difficult' but said the opportunity at Morgan Stanley was 'spectacular'.
'No one thought this would happen,' he said, referring to Mack's return to the investment bank. 'B-M is a great firm with a great global footprint and all the assets you would want in global communications and much more. I'd be lying if I said this decision was easy.'
Nides, who had never before held a position with a PR agency, arrived at B-M last November to succeed retiring CEO Chris Komisarjevsky (PRWeek, 22 October 2004).
He was formerly global chief administrator at Credit Suisse First Boston.
He will now have the same title at Morgan Stanley.
B-M's appointment of an outsider at such a senior level came as a surprise to an industry more accustomed to growing its own talent.
Nides denied his inexperience had any relation to the brevity of his tenure.
'I can't talk about myself, but I connected to people in a good way and I never would have left had it not been for this particular situation,' he said.
No successor has yet been named but Nides told PRWeek he has promised WPP chief executive Martin Sorrell that he will remain with the agency until one is found.