Biden, who spent the last five decades in Washington but never lost touch with his working-class background, is scheduled to face union workers in Pittsburgh on Monday as part of the rollout tour, the person said, speaking on the condition of anonymity to disclose private conversations.
While he may be popular with the white working-class in the Midwest, it's unclear if Biden will appeal to the more liberal voters who tend to have outsized sway in Democratic primary contests.
His decision largely settles the crowded and diverse Democratic presidential field at 20 candidates, including six women, five people of color and one member of the LGBTQ community. Biden would be the most experienced politician in the race, and the second-oldest, after 77-year-old Bernie Sanders.
A handful of lesser-known Democrats, including Montana Gov. Steve Bullock, could join the race in the coming weeks or months, but Biden's decision is considered the final major piece as voters, donors and elected officials alike begin to pick their favorites.
"Come on in, the water is warm Joe," California Sen. Kamala Harris, another 2020 contender, laughed on Tuesday as she campaigned in New Hampshire. "I adore Joe Biden and I think he has to make whatever decision is best for him."
Biden, who has run for president twice before with little success, will look to organized labor for support early on.
The largest firefighters union is preparing to formally endorse Biden this week, with group leaders saying they will be "investing" heavily in the former vice president's anticipated bid.
The board of the International Association of Fire Fighters will meet this week to vote on the endorsement. They plan to announce it publicly early next week.
IAFF represents 316,000 full-time firefighters across the U.S. Harold A. Schaitberger, the union's general president, said the group will help Biden raise money. It will also launch an outside group that is expected to be able to raise and spend unlimited sums supporting his candidacy.
"I always remind everyone that we are everywhere there is a blinking light or traffic light," Schaitberger said. "We have infrastructure and capability, whether it's in the neighborhoods, or whether it's working to develop caucus attendees in Iowa. Our union is very strongly resourced and we will be investing."
One of the most recognizable names in politics, Biden served for two terms as Barack Obama's vice president after nearly four decades as a senator from Delaware. His high-profile, working-class background and connection to the Obama years would help him enter the race as a front-runner, though he faces questions about his age and whether his more moderate record fits with a party that has become more liberal.
Biden spoke at an IAFF gathering in Washington last month. At the time Schaitberger said the union would be "all in" for Biden if he runs. He also acknowledged that many rank-and-file members supported President Donald Trump in 2016.
Biden, Schaitberger argued, is better positioned than other Democrats to win in the Midwest, which flocked to Trump in 2016.
Associated Press writers Marc Levy in Harrisburg, Pennsylvania, and Hunter Woodall in Manchester, N.H., contributed to this report.