The university announced the gift from the former Hoyas star on Thursday, Green's 28th birthday. He helped lead Georgetown to the Final Four in 2007 and was the No. 5 overall pick in the NBA draft that year.
Green's donation will go toward the John R. Thompson Jr. Intercollegiate Athletics Center, which is named after the former Hoyas Hall of Fame coach. It's a $62 million project that will be completely supported through philanthropy.
"I'm very fortunate to be in a position to give back to the university and to the program that has done so much for me," said Green, who earned his degree in English, with a minor in theology, from Georgetown in 2012.
Earlier in the week, former Georgetown All-American Patrick Ewing and sports agent David Falk announced a $3.3 million contribution toward the athletic facility.
The Associated Press contributed to this report.