Former Vice President Joe Biden will announce his presidential bid Thursday morning with an online video, two sources close to Biden with direct knowledge of the planning confirmed to NBC News.

Biden will then appear in Pittsburgh on Monday for an event at a local union hall, NBC News has learned. Biden will then embark on a tour of the four early voting states — Iowa, New Hampshire, South Carolina and Nevada — in the following weeks.

The former vice president finds himself atop of many early primary polls. The RealClearPolitics polling average has him at just above 29 percent, with Vermont independent Sen. Bernie Sanders in second place at about 22 percent.

News that Biden is set to announce on Thursday comes after months of suspense over whether he would join the primary field, although it appeared to be all but certain in recent weeks. Even the date of his announcement video appeared to be in flux, as other outlets reported it would be released on Wednesday.

"My intention from the beginning was, if I were to run, (I) would be the last person to announce," Biden said last last week. "We’ll find out whether I can win in a primary."

This will be Biden's third run for the White House. Both prior campaigns — in the 1988 and 2008 election cycles — ended well before the Democratic primary process had played out. After that 2008 bid, Barack Obama tapped Biden as his running mate, and Biden went on to serve as Obama's vice president for eight years after a more than three-decade career in the Senate representing Delaware.

Since President Donald Trump unexpectedly won in 2016, Biden has been a sharp critic of the president's foreign policy and political rhetoric and campaigned across the country for Democrats in the 2018 midterms. But Biden is faced with a leftward push among some of his Democratic primary competitors that he has been reluctant to join.

Biden's lengthy record in Washington has already come under intense scrutiny ahead of his expected bid. He authored the Violence Against Women Act, helped pass an assault weapons ban and came out in favor of same-sex marriage before Obama, but he also voted in favor of authorizing the Iraq War, was a lead author of a contentious 1994 crime bill and, as Senate Judiciary Committee chairman, presided over Justice Clarence Thomas' confirmation hearing to the Supreme Court — which included handling Anita Hill's testimony that Thomas sexually harassed her, which he denied.

Then, just weeks before the anticipated launch of his campaign, Biden was criticized for what a former Democratic nominee for Nevada lieutenant governor described as unwelcome physical contact at a 2014 campaign event. Soon after, other women described similar interactions.

Responding to those statements, Biden acknowledged in an online video this month that "social norms are changing" and what he viewed as "gestures of support and encouragement" sometimes made people uncomfortable. He vowed to "be more mindful and respectful of people's personal space."