The letters were written while Jagger was filming "Ned Kelly" in Australia between July and August 1969, The Guardian reported Friday.
The lot of letters is expected to fetch between $111,000 and $159,000 at Sotheby's on Dec. 12.
"They are much the best letters by Jagger to have come up at auction," said the Sotheby's manuscripts specialist, Gabriel Heaton. "He has a strong sense of irony about himself and what it is to be a superstar. He is very self-aware but think about it -- in order for someone to stay sane with what was going on in all of his adult life you would need to be pretty centered."
Hunt, the mother of Jagger's eldest child, said she is selling the letters because she's "broke."
"Someone will protect them [the letters] and someone who protects them will protect me because I will make enough money from the sale to repair my house in France and if I fall down tomorrow with a stroke, which is happening with several of my friends, my daughter doesn't have to say 'What are we going to do about mom?' "