The agency will consist of two divisions: Modus Publicity, which will focus on fashion, and ModusDowalWalker, specialising in health and beauty.
Unusually, the combined entity will be jointly led by four directors, with no named overall boss. The quartet are: Diana Hall and Julian Vogel, formerly of Modus, and Dowal Walker founders Owen Walker and Fiona Dowal.
Forty-strong Modus Publicity has been in business since 1987, while Dowal Walker - which has seven staff - launched in 1994. All staff are being retained.
Their combined client list includes Calvin Klein, Lacoste, Esprit, nails inc, Aveda, NARS and Philosophy. The agency also this week won an account with skincare brand Murad, after a three-way pitch.
The merger follows months of speculation that the deal was on the cards (PRWeek, 18 March).
Six-strong fashion agency Judy Bennett PR (formerly known as Jean Bennett PR) is to cease trading on 30 September, after 43 years in business.
The agency's MD, Judy Bennett, is to take some time off and plans to then work as a freelancer.
The agency was founded by Bennett's sister, Jean, in 1963. It was well known during the 1970s and 1980s, when it worked on the launch of Sock Shop, and with designer Jeff Banks.
Recent clients include Karen Millen, Ravel, Whistles, Pretty Polly tights and Playboy apparel.