The letter to be auctioned at Christie's in London was expected to fetch nearly $100,000, the Scotsman reported Wednesday.
The clemency petition was written on June 16, 1618, the report said. But it fell on deaf ears and Raleigh was beheaded in Whitehall four months later.
Historians say the letter throws light on Raleigh's gamble in returning to England from the New World.
In 1603, Raleigh had been accused of plotting against the king and sentenced to death, a sentenced commuted to life imprisonment. In the disastrous expedition to the Orinoco in 1616, Raleigh lost his fleet, his son was killed and, most importantly, he razed a Spanish settlement, in direct defiance of the king who wanted to foster good relations with Spain. The death sentence was then re-stored.