For Buffett, the deal represents an unusual teaming with private equity for a major acquisition.
He told CNBC that 3G approached him with the idea in December and that it was "my kind of deal."
He has been on the hunt for a major purchase, something worth $20 billion or more.
Buffett said Thursday that Berkshire's piece of the Heinz purchase was $12 billion to $13 billion cash, for a mix of common and preferred equity.
Heinz said the deal would be financed with cash from Berkshire and 3G, debt rollover and debt financing from JP Morgan and Wells Fargo.
Buffett told CNBC that Berkshire and 3G would be equal equity partners. The price represents a premium of 19% to Heinz's all-time high, and the stock actually rose above $72.50 in premarket trading.
Heinz's shares soared 20% to $72.59 in premarket trading on the New York Stock Exchange.