John Boehner backed out of a deal to join a marijuana lobbying group — but only after he allegedly stole its data and talking points to form another, pro-weed lobbying outfit of his own, an explosive lawsuit claims.

The former House speaker signed an agreement in March 2018 to become co-chair of the 10 Campaign — a weed legalization group that takes its name from the 10th Amendment of the US Constitution, which establishes states’ rights, according to the suit filed in the Superior Court for the District of Columbia.

Less than a year later, in February 2019, however, Boehner announced he was launching a new group called the National Cannabis Roundtable, revealing he had tapped Kathleen Sebelius, the former health and human services secretary, as a co-chair.

The powerful, Washington-based law firm Squire Patton Boggs, where Boehner is a partner, was also a strategic adviser on the project, according to the suit filed against both Boehner and the firm by 10 Campaign’s founder and executive director, James Pericola. He alleges that Boehner’s group, which went on to become a lucrative business, cut him out of its profits despite it being nothing more than a “repackaged version” of his own.

“Boehner served to legitimize the industry … and paved the way for other politicians, elected officials and influencers to come to the table after years of opposition to cannabis legislation,” the suit alleges. “And he did it by intentionally misleading Pericola.”

In an exclusive statement to The Post, Pericola said, “I did not make this decision lightly and realize we are taking on Goliath, but the truth matters and we look forward to our day in court.”

According to the suit, Pericola approached Boehner’s aides and Squire Patton Boggs in early 2018 after Attorney General Jeff Sessions struck down the Cole Memorandum — a 2013 rule that ended federal prosecution of marijuana-related offenses in states where weed was legal.

Pericola saw Boehner, with his cigar habit and conservative base, as the perfect man to normalize weed, according to the suit. Pericola reasoned that if Boehner, who as of 2015 said he was “unalterably opposed to the legalization of marijuana,” could change his mind, so could everyone else, according to the suit.

Squire Patton Boggs expressed enthusiasm for the idea, and Pericola began sending the firm proprietary materials after the parties signed non-disclosure agreements, according to the suit. As of early April 2018, the group had assembled promotional materials to launch the 10 Campaign with Boehner as co-chair.

In addition to states’ rights, conservative-friendly talking points included arguing that marijuana can help veterans with physical pain and PTSD, ease the opioid epidemic and treat epilepsy, aid criminal justice reform, and increase tax revenue. The 10 Campaign also provided polling data that showed most Americans favored legalizing weed.

Then, on April 11, 2018, Boehner tweeted he’d be joining the board of Acreage Holdings, an early investor in marijuana. The company — now publicly traded in Canada — is involved in the growing and dispensing of weed.

Pericola claims he tried to move forward with the 10 Campaign despite Boehner’s tie-up with Acreage, but that he was rebuffed by Boehner and Squire Patton Boggs. Meanwhile, Boehner’s rash of media interviews after the announcement mirrored the 10 Campaign’s talking points.

“I found myself like a lot of Americans over the last 10 years or so beginning to look at this issue a little differently,” Boehner said on NBC’s “Today” show, after announcing his Acreage board seat, according to the suit. “In the United States, each of the states has a right to make that decisions … My position is the states should decide.”

Boehner’s about-face on cannabis was so dramatic that the SXSW conference in Austin, Texas, asked him to come speak about it in March 2019. At the fireside chat, the moderator told Boehner that his pot bombshell was “so seismic,” he’d never forget where he was when he heard the news.

The announcement even led weed-smoking comics Cheech and Chong to say “Pot’s Over” now that someone as boring as Boehner was on board with legalization.

Since the announcement, Boehner has been living the “high life,” raking in millions of dollars in fees, the suit claims. Pericola’s attorney said that while he couldn’t specifically determine the extent of Boehner’s cannabis-related earnings, he estimated it was at least “seven figures.”

Boehner and SPB did not respond to repeated requests for comment.