The deal will save older Americans US$1.5 billion and the Medicare federal health insurance scheme US$6 billion in the first year, the statements added.
Harris has already made bringing down high prices a key plank of her election campaign and will hope the announcement on medicines will win over voters who have long been struggling with inflation.
US residents face the highest prescription drug prices in the world, leaving many people to pay partly out of their own pocket, despite already exorbitant insurance premiums.
The pair will hail the drug price deal at an event in Maryland – their first outing together in the aftermath of Biden’s withdrawal from the election following a disastrous debate with Trump.
Biden highlighted Harris’s role, saying the “historic milestone” was only possible because the post-Covid Inflation Reduction Act was passed by Congress after his vice-president cast a tiebreaking vote in the Senate.
Harris added in her statement: “President Biden and I will never stop fighting for the health, well-being, and financial stability of the American people.”
It comes a day before Harris is due to set out her own economic agenda in a speech on Friday, and ahead of her star turn at the Democratic National Convention next week.
The United States’s first female, Black and South Asian vice-president has already breathed new life into the Democratic Party after the trauma of Biden’s departure.
But while she has wiped out Trump’s lead in the opinion polls and drawn huge crowds to her rallies, she has yet to spell out her policies beyond broad brush strokes.
That includes largely adopting Biden’s economic agenda so far, including his vows to eradicate “junk fees” and bring down housing costs.
Harris is also trying to keep some distance from Biden’s policies and set out her own stall.
The news outlet Axios reported on Wednesday that Harris wants to “break with Biden on issues on which he’s unpopular”, with rising prices being top of the list.
02:07
US vice-presidential hopeful Tim Walz slammed by Trump supporters for China connection
US vice-presidential hopeful Tim Walz slammed by Trump supporters for China connection
Inflation has dogged Biden’s presidency, with many voters rating him poorly on the economy despite otherwise good numbers for jobs and growth.
Conversely, more people now trust the vice-president to handle the economy than Trump, at 42 per cent to 41 per cent, according to a Financial Times and University of Michigan poll.
Before she took the reins, Biden was at 35 per cent, while Trump’s number is unchanged.
Trump will try to steal their thunder as he holds a press conference shortly after the event.
The Republican former president, who survived an assassination attempt on July 13, has so far struggled to deal with an upended election campaign after the Democratic Party’s candidate switch.
Trump gave a speech that was meant to focus on the economy on Wednesday – but ended up veering off into personal insults, calling Harris a “crazy person,” Biden “stupid” and Harris’s running mate Tim Walz a “clown.”