In a video message released on Friday by NowThis News, the two actors, who will be seen together for the first time in director Quentin Tarantino's next "Once Upon a Time in Hollywood", talked about the importance of voting in November 6 elections.
"The future of our country will be decided this week. Elections don't just matter when voting for president," said 43-year-old DiCaprio.
He said issues like gun safety laws, clean water and air, immigration policy and health care are at stake.
Pitt, 54, said, "Statehouse elections will determine the future of climate change, criminal justice reform, education funding, LGBT equality and even your ability to vote."
"All of these races and ballot measures are chances to decide on the direction of our country. We, the voters, have the power to decide all of this," DiCaprio added.
The two stars then told viewers to visit TheLastWeekend.org to see how they can get involved and help.
"There's no denying the importance of this election, please make your voice heard," Pitt concluded.
(With inputs from agencies.)