An adviser to 59-year-old Harris's campaign said the report would conclude: "She possesses the physical and mental resiliency required to successfully execute the duties of the presidency."
The US vice president's team aims to put the spotlight on the physical health and mental acuity of 78-year-old former president Trump, who has so far refused to release any detailed medical information.
Republican Trump became the oldest presidential nominee in US history after 81-year-old President Joe Biden withdrew from the White House race in July.
Biden passed the torch to Harris after a disastrous debate against Trump raised concerns in the Democratic Party about his own mental sharpness.
But Trump's apparent vitality means that his age has not so far weighed against his chances in the polls, in a knife-edge battle with Harris in the November 5 presidential election.
Harris's campaign drew attention to a recent series of articles in the New York Times that raised concerns about the fact that Trump had failed to disclose basic information about his health.
The newspaper also published an analysis of Trump's language showing that his speeches are increasingly long, "confused" and vulgar, which it said were seen by experts as a possible sign of cognitive change.
Trump insists he is fully fit, but he has not released any full medical report for his campaign.
In late 2023, Trump released a note from his former White House doctor declaring him to be in "excellent" health, but it was short on details and did not say what tests Trump had undergone when he had a physical in September 2023.
The same doctor, Ronny Jackson, issued a statement in July after Trump's ear was wounded by an assassin's bullet at a rally in Pennsylvania, saying the former president was doing well.
Trump meanwhile boasted about a cognitive test he had underwent with Jackson while president in 2018 -- but then immediately flubbed his doctor's name, calling him "Ronny Johnson."
If Trump wins the election in November, he would be 82 at the end of his second term in the Oval Office.
