The Clinton campaign said Monday that Sanders will join the former secretary of state at a high school in the town of Portsmouth “to discuss their commitment to building an America that is stronger together and an economy that works for everyone, not just those at the top.”
Sanders has yet to endorse his former rival for the Democratic nomination.
But the New York Times reported last week that Sanders would appear at a Clinton rally Tuesday in New Hampshire, and that he would formally endorse her.
The daily said the anticipated pledge of support is the result of weeks of talks between the two campaigns aimed at unifying the party.
Clinton clinched enough delegates to secure the nomination in early June, after a yearlong battle with Sanders, a senator from Vermont.
But the feisty self-described democratic socialist nevertheless has refused to concede defeat to his more moderate rival, although he has said he will vote for Clinton and will do anything to help defeat Republican Donald Trump.
Sanders has been negotiating with the Clinton campaign to ensure that his ideas are part of the party platform presented at the Democratic convention later this month, when Clinton is formally nominated.
Party officials met over the weekend in Orlando, Florida to finalize the Democratic platform for the November election.
The two sides reached agreement on language concerning climate change, health care and raising the minimum wage in America to $15 per hour. They failed, however, to reach common ground on the Trans-Pacific Partnership trade accord, media reports said.