The consultancy blamed economic reasons for its decision to step down from the US investment bank brief, which it won last September.
Edelman Asia-Pacific president Alan Vandermolen said: 'We did not think the account was commercially sustainable for us in Hong Kong.'
The agency will continue to provide corporate communications support for the investment bank's South Korea operations, despite the recent decision.
Lehman Brothers confirmed Edelman would be replaced across the Hong Kong region by Gavin Anderson & Co, which is already retained as the bank's agency of record in Japan.
Tokyo-based Asia-Pacific corporate communications head Jackie Kestenbaum would not comment on the rationale behind the change of agency.
But she said she was 'happy with both relationships' and confirmed Edelman would continue working on the business in Seoul.
Edelman was originally selected after Kestenbaum's appointment in June last year.
Under the original deal, Edelman's Asia-Pacific associate director of financial communications Rhea McGraw had been seconded to work in the Lehman Brothers Hong Kong office on a weekly basis, handling regional media relations and reporting to Kestenbaum.
Gavin Anderson Asia CEO Richard Barton said this arrangement would not continue as part of the new appointment.
Kestenbaum had previously outsourced the Hong Kong corporate communications post to McGraw, putting on hold plans to recruit for the role.
McGraw joined Edelman last year from satellite-enabled broadcast operator SpeedCast Hong Kong.