Nazir will partner with Chris Reed, who currently heads up Fishburn Hedges' digital and social media team, to lead the yet-to-be-named agency.
The agency will begin business operations on November 17, with a formal launch planned for early 2009.
Nazir, with 14 years' experience in digital marketing, has been recruited from her current role as head of planning for MRM Worldwide, with clients including Intel, Mastercard, BSkyB and Microsoft.
Previously she was business director at Wunderman Interactive, where she was responsible for managing Ford across Europe, the Middle East and Africa.
Neil Hedges, Fishburn Hedges Group chief executive, said: "The digital environment has created new opportunities and challenges for our clients. We have big growth plans for our new agency, which will go beyond what each of our existing businesses is currently managing, digitally speaking.
"Hiring Mobbie and launching our digital business is our group's most exciting and important development for years. We've been keen to develop this new agency with a top-quality, experienced partnership, and with Mobbie and Chris as joint managing partners we're certain we've found the right combination."