Zagat, founded in 1979, is well-known for its user-generated reviews and pocket-sized guides. In addition to restaurants, it reviews hotels, bars and other accommodations in more than 100 cities.
The deal comes as federal regulators have begun to examine Google more closely for potential anti-competitive behavior.
The Federal Trade Commission is investigating the Internet giant, and on Sept. 21, Google Executive Chairman Eric Schmidt will testify at hearing of the Senate Judiciary Committee's antitrust subpanel.
The deal is not the first time Google has shown interest in expanding its local review presence. In 2009, its plans to buy review service Yelp fell through.
Yelp has since become one of Google's most vocal critics, accusing the company of stealing its content by using snippets of reviews on its Google Places service.
The deal is Google's second major purchase in recent weeks. Last month, it bought phone-maker Motorola for $12.5 billion.
An announcement on Zagat's website jokingly gave the deal a perfect score of 30.