It means that they have made donations to the school, including pledges, totalling more than £100,000 ($131,000).
The donations fund bursaries for children whose parents would not otherwise be able to send them there.
The disclosure, reported by Sky News, comes at a time when Mr Sunak has been accused of being out of touch with ordinary families struggling with the rising cost of living.
He has faced criticism, including from some Tories, of not doing enough to help those on low incomes in last month’s spring statement.
“Rishi and his wife have donated to numerous charities and philanthropic causes for many years and will continue to do so,” said a spokeswoman for the Chancellor.
“These donations are made to help fund scholarships for children who would not otherwise have the opportunity to go to Winchester.”
For Labour, shadow education secretary Bridget Phillipson said Mr Sunak should end tax breaks for private schools like Winchester and use the money raised to invest in the state education system.
“Britain should have the best state schools in the world.
“But after 12 years of Tory neglect, four in 10 of our children leave school without the qualifications they need,” she said.
“Rishi Sunak has already said that he is ‘maxed out’ on how much support he can give to our state schools, but he continues to hand out billions in taxpayer subsidies to elitist private schools.
“Labour would end the tax giveaway Rishi Sunak hands out to his old boys’ network and use the money to improve every state school instead, ensuring everyone leaves education ready for work and ready for life.”