The audit and financial advice company, Ernst & Young, is set to merge with Andersen Switzerland.
The new company, which will operate under the name, Ernst & Young, will employ 2,500 people with an annual turnover of SFr520 million ($314 million). It will provide services including audit, risk advice, and legal and fiscal assistance.
The merger should enable the new Ernst & Young to challenge PriceWaterhouseCoopers, the current Swiss market leader.
Wednesday's announcement by the two companies surprised market observers. At the beginning of this month, Andersen Switzerland said it had entered negotiations with its competitor, KPMG.
KPMG said in a statement that it regretted Andersen's decision, which puts an end to a merger planned for October 1.
The move, which does not involve any job cuts, still requires approval from the Competition Commission.
Andersen is in the process of being broken up globally following its involvement in the collapse of the United States energy giant, Enron.
swissinfo with agencies