Sony struck a deal with Google in March, but at the time its library only housed around 500,000 titles.
The e-books are free and void of copyright, available for two Sony Reader models, accessed by downloading the Google Books software.
Sony said the addition of Google's library gives it the largest, most comprehensive array of electronic books available in the market.
In comparison, Amazon offers about 300,000 titles for its Kindle e-reader, while newcomer to the market Barnes & Noble announced earlier this month opened up its online bookstore, with about 700,000.
The announcement is the latest in a series of industry moves as the three early adopters grapple for a foothold in the nascent e-book market.
Sony was first out of the blocks in 2006 when it released the Reader, however Amazon has managed to steal much of the media spotlight with the Kindle - despite that fact that both company's devices are out of reach for most consumers, starting at about £300 each.
The market has also been held back by the various copyright policies of the devices, which runs the risk of confusing customers.
For example, titles purchased in through the Kindle Store can be read on the Kindle and iPhone, but not on any other device, while Barnes & Noble's books can be read on the iPhone and BlackBerry's, but not on the Kindle. Sony's Reader is exclusively propriatery.
Consumers are also spoilt for choice in the UK, with the Reader largely the only available device. However, that is due to change once Amazon releases the Kindle in the UK, which is expected within a couple of months.
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