Mr Romer-Lee served as managing director of Morningstar's investment consulting operation in Europe while Mr Whittingham worked as managing director of Morningstar OBSR in Europe.
Both men worked together at research firm OBSR (Old Broad Street Research) before it was taken over by Morningstar in 2010. Mr Romer-Lee had been co-founder while Mr Whittingham was its development director.
Their roles will be taken over by chief executive of Morningstar UK Geoff Balzano and Hal Ratner, chief investment officer for Morningstar Investment Management in Europe until the firm appoints a replacement.

Mr Romer-Lee said: "Now the OBSR business has been integrated with Morningstar, Nigel and I recognise that it is time for us to take a break. We are incredibly proud of the work we have done to serve our clients and win business as part of Morningstar."
Mr Balzano said: "We have worked side by side to integrate and grow our consulting and research business in the UK and across Europe.
"We have a team of talented individuals on board and are pleased that Richard and Nigel will stay with us during the coming weeks to ensure a smooth transition for our clients. I have great respect for both of them and wish them the very best."