The Sunday Times of London said Valerie Eliot responded to a London Library appeal for money with the generous donation and it will be used to help finance the construction of an annex.
The new library could potentially become the largest independent lending library in the world and will bear the name of the Nobel Prize winner, the newspaper said.
The donation will likely be funded through royalties paid to the Eliot estate from composer Andrew Lloyd-Webber, who reportedly used one of Eliot's works as inspiration for his musical "Cats."
The Times said Eliot served as president of the London Library for 13 prior years prior to his death in 1965 and reportedly once said "if this library disappeared, it would be a disaster to the world of letters."
The estimated cost to build the library annex is more than $51 million. To date, more than $32 million has been raised.