Agency sources suggested that the deal could be completed as early as next week and is likely to lead to the creation of an agency led by a combination of MRM and Meteorite management.
Mike Cornwell, the chief executive of MRM London, Meteorite's chairman, Hugh Bishop, and its managing director, Debbie Smith, are all expected to have senior roles.
The client lists of the agencies seem complementary, with MRM handling accounts including General Motors, BSkyB and Johnson & Johnson. Meteorite, which has strong digital and social media credentials, works for the likes of Breakthrough Breast Cancer, Homebase and Costa Coffee.
Meteorite was founded 12 years ago and employs around 70 staff. Before launching the agency, Bishop held senior marketing positions at Levi's and Burton Group, while Smith was the managing director of WPP's integrated agency PCG.
The negotiations are the latest indication of an aggressive acquisition drive by McCann Worldgroup. Last month, it acquired the interactive design agency AllofUs, which retained its name but now sits within the McCann London building.
Meteorite and McCann Worldgroup declined to comment.