Representatives of Clinton, Sanders and the Democratic National Committee will discuss the platform this weekend in Orlando, Florida.
Citing three Democrats who have been involved in the planning, the Times said the endorsement was partly the result of daily talks between the candidates' campaign managers about bringing them together and advancing Sanders' policy priorities.
After repeatedly pledging to continue his campaign until the convention, the Vermont senator has appeared increasingly open to backing Clinton in recent weeks.
Last month, Sanders told supporters in an email that "we are going to take our political revolution into the halls of the Democratic National Convention in Philadelphia where we will fight to place a $15 minimum wage, opposition to (the Trans-Pacific Partnership), and a ban on fracking directly into the Democratic platform".
Clinton on Wednesday announced a proposal to offer free college tuition to students of families making less than $125,000 per year by 2021, a shift Sanders, who championed eliminating public college tuition, called "revolutionary".
The Sanders camp would also like to see Clinton commit to pushing Congress on adding a public option to the Affordable Care Act.
Clinton secured enough delegates to clinch the Democratic nomination just over a month ago, but Sanders has stayed in the campaign - though he kept a lower profile.
"With each passing day", Garin said of a Sanders endorsement, "it gets a little bit more anti-climatic". "I think the time is coming to resolve this and to prepare for a convention where hopefully he will give a powerful speech".
Sanders supporters passionately rally for the candidate when he spoke at the Florida State Fairgrounds in March.
Sanders, on average, was creaming Trump by double-digits, while Clinton, while ahead, had a much more narrow lead that the billionaire has sometimes cut into.
As for Clinton, she received an all-clear from FBI Director James Comey, who said publicly on Tuesday that he would recommend to the Department of Justice that no criminal charges be filed against the former secretary of state for mishandling government secrets.
Sanders all but confirmed that he would endorse Clinton in an interview with Bloomberg on Thursday. The campaign says additional details will be released soon. Elizabeth Warren and other prominent Democratic leaders in officially supporting Clinton's campaign.
Obama endorsed Clinton during a joint event in North Carolina on Tuesday, and she is set to campaign with Vice President Joseph R. Biden Jr.in Pennsylvania on Friday.
We're right there with you, Bern!