Andrew Yang, who unsuccessfully sought the presidency and the New York City mayoralty as a Democrat, will launch a third party next month — an announcement tied to the publication of his new book, a source close to Yang confirmed to The Post. 

The move by Yang, best known for his advocacy of a monthly universal basic income of $1,000 for every American adult, was first reported by Politico Thursday.

Yang’s new book "Forward: Notes on the Future of Our Democracy" comes out on Oct. 5.

The tome, published by Penguin Random House subsidiary Crown, is billed as "a powerful and urgent warning that we must step back from the brink and plot a new way forward for our democracy" and promises to identify "‘priests of the decline’ of America, including politicians whose incentives have become divorced from the people they supposedly serve," according to an online description.

The book’s website includes blurbs from Dallas Mavericks owner Mark Cuban ("a vitally important book"), New York Times opinion writer Kara Swisher ("Yang does not just give us a laundry list of intractable problems, but shows how we can find solutions if we think in new ways and summon the courage to do so") and CNN contributor Van Jones ("Yang once again proves he is a necessary and powerful voice").

Yang was one of the first Democrats to enter the 2020 presidential race, filing papers to run in 2017. His campaign drew attention for his universal basic income pitch, his warnings about the automation of the US economy and his boisterous social media supporters — known as the "Yang Gang."

However, Yang could not convert that enthusiasm into votes and he dropped out of the race after finishing sixth in the Iowa caucus and eighth in the New Hampshire primary.

Yang then turned his attention to this year’s Democratic mayoral campaign. After holding a large lead in early polls, his campaign faded in the final weeks before the June 22 vote. After initial results on primary night showed him receiving the fourth-most first-choice votes, Yang conceded defeat, acknowledging to supporters that "there was so much about New York City I did not know."

It was not immediately clear what Yang will call his new party, nor was it clear what offices it would target in future elections.

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Requests for comment to Yang by The Post went unanswered Thursday. However, the tech entrepreneur tweeted "Excited" in apparent response to the initial Politico report.