Four has acquired 60 per cent of the agency’s equity, while shareholders including chief executive Dotti Irving and MD Liz Sich will retain 40 per cent.
The agency will be renamed Four Colman Getty and will join Four Communications' PR, public affairs, digital services, sponsorship, media and marketing practices. It will move into the group's Leicester Square HQ in the coming weeks.
Four Colman Getty is expected to have a combined annual fee income in excess of £3 million, with clients including The Man Booker Prize for Fiction, Library of Birmingham and the RHS Chelsea Flower Show.
Following the acquisition, Four Communications Group will have total income of some £12 million.
Last year, Four acquired travel specialist agency BGB and opened offices in Edinburgh and Oman.
Four Communications Group chief executive Nan Williams said: ‘We are committed to an intelligent acquisition programme of top notch independent companies which are leaders in their field. The energy, heritage and passion of Colman Getty makes it one of the most impressive independent consultancies in the UK today.’
Irving said: ‘After 25 years of running Colman Getty, it has been a big decision to move into a bigger arena. We wanted to merge with Four because the people there have the same commitment to their clients and their people as we have at Colman Getty.'
Known for handling culture and campaigning accounts, Colman Getty is in its 25th year.
Irving and Sich will continue to run the agency. Irving will join the operating board of Four Communications Group.
After the acquisition, Four Communications Group will have more than 150 staff in the UK and the Gulf.