Whitehead Mann said the combined businesses were expected to generate annual revenues of more than 75m (€122m), and employ about 400 professional and support staff. A source close to the deal said no redundancies were expected.
The firm made the announcement alongside its interim results for the six months ended September 30, which showed operating profits up by 40% to 4.3m.
Despite the fall in demand in investment banking search amid the economic downturn, Whitehead Mann has been keen to strengthen its global presence in financial services. Baines Gwinner offers strength in this area as well as an established legal search capability, in Hong Kong as well as in London.
Baines Gwinner's New York office will fold into Whitehead Mann's presence there, which expanded last year through its purchase of Pendleton James, the boutique financial services headhunter.
Jonathan Baines, founder and chief executive of Baines Gwinner, is to become co-chairman of the financial services group and head of Asia at the enlarged Whitehead Mann Group.
Amy Russo of Baines Gwinner, whose team will add new capabilities in debt and equity capital markets, will be head of financial services in New York. Anthony May, who has led the expansion of Baines Gwinner's legal search expertise, is to be business unit leader of professional services. Karin Barnick will coordinate asset management for Europe.
Peter Wisher is to retain responsibility for the financial training arm set up by Baines Gwinner which, along with the career management firm BG Careers, will remain largely unchanged.
Although eyebrows are being raised in the recruitment industry as to the timing of the deal because of the economic downturn, the two firms are complementary.
Baines Gwinner has been on the lookout for a way of extending its global reach ever since its plans for a merger with the global search firm Heidrick & Struggles were aborted last year.
Whitehead Mann has been keen to expand in Asia and continue its strategy to transform itself from a UK-centric search firm into a global leadership consultancy.
In a statement likely to ring in the ears of many headhunters in the current downturn, Baines Gwinner said that it "recognises that in a global market it makes good strategic sense to tie its future to a major brand."