SNS Group now has four offices, adding W&B's bases in Cambridge and Eindhoven, Netherlands, to existing sites in Kent and Surrey.
W&B managing director Simon McKay becomes MD of SNS in Cambridge, while SNS group chairman Len Scannell keeps that role.
On losing the W&B brand, SNS spokesperson Theresa Prevost said: 'We took the decision that we would want to harmonise across the group and quickly establish a consolidated brand for the whole group.'
In last year's PRWeek Top 150, W&B - which has grown its fee income by almost 500 per cent since 1996 - held its place as the fastest growing agency over five years.
The new group will provide a range of B2B marcoms services, including PR, advertising, design, new media, exhibition and event management.
W&B will transfer its clients to SNS. They include Philips Semiconductors and Philips Medical Systems.