Titled "Go From There," the commercial, which aired as the 2020 World Series began on Tuesday, called on Americans to come together and to put their differences aside.
As a piano rendition of the star spangled banner plays, Mr Elliot, whose appearances in "A Star is Born” and "The Big Lebowski" have made him a household name, says “'There is only one America.”
He continues: “No Democratic rivers. No Republican mountains. Just this great land, and all that’s possible on it with a fresh start,”
“There is so much we can do, if we choose to take on problems, and not each other. And choose a president who brings out our best,” says the actor, who does not appear in the ad.
“Joe Biden doesn't need everyone in this country to always agree. Just to agree. We all love this country. And go from there”
“This is the best Biden ad so far. Absolutely awesome. Thank you, Sam Elliott,” wrote Democrat and ex-council leader, Jon Cooper, on Twitter.
Another user wrote: “That Sam Elliott Biden ad might be the best piece of political advertising I’ve ever seen.”
Mr Elliott said in a 2017 interview that Donald Trump’s election win was "mind-boggling"
"I think Trump won because he didn't have someone running against him that was electable," he told Metro. "But he spoke to that vast whole out there that had been neglected forever."
The actor’s campaign debut comes after a dozen Hollywood stars have endorsed Mr Biden, the Democratic presidential nominee, in recent weeks.
They include Jennifer Lopez, Dwayne "The Rock" Johnson, and Taylor Swift, as well as several cast reunions - including “The West Wing,” “Veep” and “Parks and Rec” - who have raised money for Mr Biden and Democratic candidates.