No money changed hands in the transaction, which involved Tulchan acquiring the 49 per cent stake of Investor Perceptions MD Simon Collins before transferring 50 per cent to Rothschild.
Rothschild is contributing its expertise and access to clients in Europe in return for its stake, according to Tulchan, which has been a shareholder in Investor Perceptions since 2010.
Agency founder Andrew Grant said: "Tulchan originally backed Investor Perceptions because we viewed the understanding of why institutional investors were or were not shareholders in companies as being critical to any efforts to manage corporate reputations. I am delighted to have the opportunity to accelerate the development of the offering through the joint venture with Rothschild."
Robert Leitão, management committee chairman, Rothschild Global Financial Advisory, said: "Rothschild's investment will allow clients a deeper insight into the views of institutional shareholders and the drivers of their investment approach.
"Operating in joint a venture means that these insights will be obtained independently and at arm's length in a manner that preserves the discretion and objectivity for which the Investor Perceptions service has come to be known, and which is entirely consistent with Rothschild’s values as a firm."