The agreement, announced Monday, will let Internet users read, search, download and copy thousands of texts published between 1700 and 1870.
It is a small step toward the library's goal of making the bulk of its 14 million books and 1 million periodicals available in digital form by 2020.
"So far we have only been able to digitize quite a small fraction of the global collection," said the library's chief executive, Lynne Brindley. "There is a long way to go."
The deal with Google, which will see 40 million pages digitized over the next three years, will offer online researchers a selection of rarely seen works from an era of social, political, scientific and technological change that took in the Enlightenment, the Industrial Revolution and the American war of independence.
The books range from Georges Louis Leclerc's "Natural History of the Hippopotamus, or River-Horse" - which includes a description of a stuffed animal owned by the Prince of Orange - to the 1858 work "A Scheme for Underwater Seafaring," describing the first combustion engine-driven submarine.
The books are more than scholarly curiosities. British Library curator Kristian Jensen said an 18th-century guide to English for Danish mariners shows "how English began to emerge from being the language spoken by people over there on that island" to become the world's dominant tongue.
Google will pay to digitize the books, which are no longer covered by copyright restrictions. They will be available on the British Library and Google Books websites.
Peter Barron, Google's European spokesman, declined to say how much the project would cost, beyond describing it as "a substantial sum."
Google has digitized 13 million books in similar deals with more than 40 libraries around the world. But its plan to put millions of copyrighted titles online has been opposed by the publishing industry and is the subject of a legal battle in the United States.
Barron said the company's goal "is to make as wide a range of items as possible" available online.
"Having richer content means people around the world are searching more for it, and that is good for our business," he said.
Last year, the British Library announced plans to digitize up to 40 million pages of newspapers dating back three-and-a-half centuries, and it recently made thousands of 19th-century books digitized in a deal with Microsoft available as an app for iPhone and iPad devices.
Google Books: http://books.google.com/ British Library: http://www.bl.uk/