It is taking on the 300 staff from Parthenon, across offices in cities including London, Mumbai, San Francisco, Shanghai, Singapore and Boston.
Neither Parthenon nor EY have disclosed the price of the deal. Clearsight Advisors worked on the transaction.
The business will be wrapped into EY’s transaction advisory services unit, advising clients on capital investment and portfolio management.
It will continue to use the Parthenon brand and be run by Parthenon’s chairman and managing partner Bill Achtmeyer.
“Together we can offer superior end-to-end consulting services from ideation to implementation,” said Achtmeyer.
“I firmly believe this combination equates to one plus one equals ten.”