Robert Thomson's letter had urged the European Commission to take a tougher approach to Google's market dominance.
But in a detailed response on its website, the search company said it "has done more than almost any other company to help tackle online piracy".
Google also defended itself against accusations that it uses its market position to stifle competition.
The Commission is currently in the process of deciding how far to curtail Google's market dominance in Europe.
Google's blog, posted by Rachel Whetstone, senior vice-president for Global Communications, argued that the internet offered more choice than ever.
"Because the competition is just one click away online, barriers to switching are very, very low," it said.
"Google is of course very popular in Europe, but we are not the gatekeeper to the web, as some claim."
News Corp had warned that some newspapers were in danger of going out of business, partly because of Google.
But Google said it "worked hard to help publishers succeed online" by generating new audiences and increasing advertising.
Countering accusations of piracy, Google said last year it removed 222 million web pages from Google Search because of copyright infringement and said that websites that regularly violated copyright were ranked lower in search results.
The riposte also points to the growing competition from mobile apps, which increasingly drive internet traffic, often bypassing Google.
The post made a cheeky final swipe at Mr Thomson's suggestion that Google's dominance was leading to "a less informed, more vexatious level of dialogue in our society".
It linked to a picture of a notorious front page of the Sun newspaper, owned by News Corp.
It was an edition of the paper from 1990 with the image of a two-fingered gesture and the headline "Up Yours Delors", referring to the then president of the European Commission, as the Sun called for a robust British approach to Europe.
Google has responded to an attack by the chief executive of News Corp, who called it a "platform for piracy".