The collection comprises thousands of notes and drafts, including from the voyage of HMS Beagle, complete with his musings on Galapagos fauna and his first recorded doubts about the permanence of species.
The collection also contains photographs of Darwin and his family, newspaper clippings, reviews of his books, Emma Darwin's recipe book, boyhood notes on birds, proofs of Origin of Species, caricatures and obituaries.
"Charles Darwin is one of the most influential scientists in history," said Dr John van Wyhe, director of The Complete Work of Charles Darwin Online at Cambridge University.
"This release makes his private papers, mountains of notes, experiments and research behind his world-changing publications available to the world for free.
"His publications have always been available in the public sphere, but these papers have until now only been accessible to scholars."
A searchable electronic catalogue has been created to help users navigate the collection, which is so large that even if someone viewed one image per minute, it would still take more than two months to see all of the material.
"Darwin changed our understanding of nature forever," added van Wyhe. "This is one of the most important collections of primary materials in the history of science."
