The AIM-listed business has paid an undisclosed sum for Edinburgh-based Line Digital.
The addition of the 13 staff means Cello now employs in the region of 190 people in Scotland. It already owns the likes of advertising specialist The Leith Agency, online marketing firm Blonde Digital and public relations business Stripe Communications.
Line, which works mainly in web design and online marketing, will be integrated with Blonde by the end of next month with the expanded business employing around 60.
Clients which Line serviced include Scottish Friendly, Standard Life, Tesco Bank, Travel Corp and the Edinburgh Fringe.
Blonde said the deal will help provide it with further scale as it seeks to grow its international client base.
Turnover for Blonde, which launched in 2006, was said to be £3.4 million for 2013 which was helped by winning business from the likes of BASF, Famous Grouse and the Scottish Government.
Its client roster also includes Nando's, Royal Mail, Glasgow2014, First Group and AG Barr.
Pete Burns, managing director of Blonde, said: "Our acquisition of Line gives us the added scale, depth and capabilities."
John Rowley, chief executive of Cello Signal, the consumer division of the marketing group, said: "We're delighted to welcome an agency of Line's technical and creative ability into Cello Signal. "This talented team will help support Blonde's growing maturity in enterprise scale design and build".
Line's managing director Ross Laurie said the deal offered an opportunity to expand more aggressively.