As well catering for weddings, conferences and banqueting, the London-based caterer plans to install one of its trademark champagne bars at the venue.
Searcys chief executive Doug Tetley said it was the balance between traditional values and fresh thinking that won his company the contract.
The caterer already holds tenancies at the Hurlingham Club, The Gherkin, The Commonwealth Club and Inner Temple.
Blenheim Palace chief executive John Hoy said the deal will help the venue towards the goal of providing a memorable experience for guests.
"You only have to look at the other venues that have placed their trust in Searcys to understand that they provide a guarantee of expertise, understanding and excellence," he said.
"Our visitor numbers continue to increase significantly and this is one of the investments we have made to ensure that the experience each and every one of those people get is absolutely top class."
Blenheim Palace welcomes around 550,000 visitors per year.
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