Billett bought the Birmingham-based auditor Barsby Rowe less than two years ago, but they have operated as separate brands within the Billett group of companies.
The move is part of a large-scale reorganisation within Billetts, which sees the company's services split into two business streams.
These two divisions are media effectiveness and sales, and marketing effectiveness - Billetts Media Consulting and Billetts International make up the former, while the recently formed Billetts Marketing Services forms the latter.
All three companies will operate as separate entities within the Billett group and have their own profit and loss sheets.
Andy Pearch, the former managing director of The Billett Consultancy, becomes the chief executive of the new Billetts Media Consulting while Barsby Rowe's former managing director, Hugh Lindsay, takes on a similar role within the new organisation.
John Billett, the chairman of the group of companies, said: "The re-engineering of our business enables us to make great strides toward becoming the number-one management consultancy in marketing communication effectiveness."