Chime chairman Lord Bell and Grandfield founder Charles Cook have agreed terms for the six-strong firm to be acquired by Chime.
Market sources believe that Grandfield will be merged with Chime's City arm, Bell Pottinger Corporate & Financial.
It is not clear how much Chime has paid for Grandfield, which counts investment bank Evolution Securities, fund management group RAB Capital and the Railtrack Private Shareholders Action Group among its clients and brought in fees of more than £1.3m in 2003.
The move comes just three months after Chime's merger talks with Incepta collapsed at the end of last year.
Grandfield founder Cook and Chime chairman Bell both declined to comment.
Grandfield's acquisition could be designed to bolster Bell Pottinger C&F, which suffered a series of high-profile departures in 2004.
At the end of January, Bell Pottinger C&F was hit by the resignation of directors Tim Grey, Katya Reynier and Jeff Watt. In 2004, the company also lost directors John Coles and Charlotte Lambkin.
Grandfield had 16 staff in 2002 but this has since fallen to six. Fee income for the firm fell by 25 per cent between 2002 and 2003, according to PRWeek's 2004 table of the UK's top 150 PR firms.
Huntsworth, which is now in advanced talks to merge with Incepta, bought a 25 per cent stake in Grandfield in 2003 as part of a referral arrangement between Grandfield and Huntsworth's IR subsidiary Global Consulting Group.
Huntsworth sold its stake back to Grandfield's management earlier this year.
Last year, Grandfield hired former Rolls-Royce director of corporate affairs Colin Duncan as a senior consultant on a part-time basis (PRWeek, 11 June 2004).