Jackson, speaking in Chicago, said he trusts that Clinton will look out for the interests of marginalized communities including refugees, immigrants and the poor.
"We trust her to work on health care, to fight for the poor ... for the willingness to fight for civil rights," Jackson said.
Jackson, who unsuccessfully sought the Democratic nomination for president in 1984 and 1988, endorsed Clinton at the site of a memorial recognizing the hundreds of children killed in the city in recent years. The civil rights activist said in a news release that he was making the endorsement independent of his non-profit organization, Rainbow PUSH Coalition, a civil rights group.
Jackson told CNN last month that he had been in touch with advisers to both Clinton and her primary challenger, Vermont Sen. Bernie Sanders, to emphasize the importance of party unity as Democrats prepare for a general election fight against Donald Trump.
Sanders "must support the winner, Hillary, over Donald Trump. That's his very public position and I hope he will hold that position," Jackson said back then.
After emerging as the presumptive Democratic nominee on Tuesday, Clinton has sought to coalesce Democratic and progressive support around her candidacy. On Thursday, President Barack Obama
, Vice President Joe Biden and Massachusetts Sen. Elizabeth Warren
threw their support behind Clinton, and on Friday, the AFL-CIO, the nation's largest labor federation, moved toward backing her