The organization got in touch with Sandler through his brother, Scott, a Manchester lawyer.
The donation was to be officially announced Wednesday when officials from the Boys & Girls Club formally kick off a $6.6 million capital and endowment fund-raising campaign called "Building Better Lives."
"This is an aggressive campaign; it's a challenging campaign, and there are probably some who question whether we can pull it off," said Executive Director Gary Frost. "But all the more credit to Adam. He sees this as a way to give back to the community where he grew up."
Frost said the capital campaign is to renovate the group's Union Street clubhouse and add a 15,000-square-foot addition.
"Our membership now is in excess of 3,000 kids, but our goal is to expand our mission to serve 4,000 kids," he said.
A performing arts center will be included in the new building, as will a learning and technology center, an exercise and weight room, a health services center and a teaching kitchen for cooking and nutrition classes, the Union-Leader said.