On his 18th birthday last year, Pascal Tessier wrote an open letter to the Boy Scouts of America. He was saying goodbye to an institution that, he said, taught him the “morals and values” that shaped the man he had become. He was saying goodbye because, although the organization had recently done away with a policy keeping gay kids out of the group, it still banned gay adults — which, now, included him.

“Today is my 18th birthday, a milestone on my path to becoming an adult and the day I am no longer eligible to be a Boy Scout because I am gay,” he wrote in August 2014. “Despite the Boy Scouts’ historic decision last year to open its ranks to gay youth, the Scouts still ban gay adults. And as of today, that means me.”

Tessier already had become a warrior in the battle against the Boy Scouts policy. In 2013, he stood on a street corner and protested its policy against gay youth. The organization later agreed to lift that ban. In 2014, he earned the Eagle Scout ranking he coveted nearly all of his life. From that moment on, he has been called the nation’s first openly gay Eagle Scout.

On Thursday, the Boy Scouts’ Greater New York Councils announced another pivotal moment: It hired Tessier as a summer camp leader — in direct defiance of the national organization’s rules. By many, it was seen as yet another victory for an 18-year-old Kensington, Maryland, man challenging a system that, by policy, excludes him.

The New York chapter said it got an application from Tessier and decided he was qualified based on his merits.

“I’m sure it won’t be a surprise to know he’s excited that he got the job,” Zach Wahls, executive director of Scouts for Equality, told The Washington Post.

“The lion’s share of the credit here goes to the New York council for stepping up to the plate,” he added. “There are a lot of chapters that say they don’t discriminate, but they just talk the talk. The Boy Scouts in New York walk the walk.”

The Boy Scouts of America has said it does not “proactively inquire” about its members’s sexual orientation so, by that logic, gay adult leaders and employees could take part as long as they keep their lives private — a system akin to the U.S. military’s old “don’t ask, don’t tell” policy. Earlier last year, an openly gay Scout leader in Seattle was booted from his position after the national organization learned he was gay.

As for Tessier, Boy Scouts of America communications director Deron Smith said in a statement that the institution’s policies regarding gay adult leaders and employees are still the same. “While we were only recently made aware of this issue, we are looking into the matter,” he said.

Tessier has been advised by fabled lawyer David Boies, who helped spearhead the U.S. Supreme Court case against California’s anti-gay marriage law. Boies told the Associated Press the new move could lead to a lawsuit between the Boy Scouts of America and its New York chapter. He has instructed Tessier not to speak to the media for now, Tessier’s mother, Tracie Felker told The Post.

“We all started this with the idea that the best resolution of this was a resolution based on conciliation and agreement,” Boies told the AP. “It is certainly a remarkable development because we now have the first openly gay scout leader employed by the Boy Scouts. We hope that is the beginning of the end, if you will, of the policy nationwide.”

Tessier’s interest in the Boy Scouts began before he was old enough to join. At age 4, he was pictured by a campfire during his older brother’s Cub Scout trip.

“I definitely wouldn’t be the person I am today without the Boy Scouts, which sounds cheesy, but it’s true,” he told The Post’s Theresa Vargas in 2013. At the time, he was worried that all his work to become an Eagle Scout might have been for nothing. He had come out in the eighth grade knowing about the Scouts policy on gay youth and adults.

“The best word would be devastated,” he said about how he would feel if he got kicked out. “I’d also feel betrayed because it’s an organization I trusted, and I put my heart into doing good for them.”

In April 2013, Tessier, then a 16-year-old high-school kid who liked poetry, ice cream and the electric guitar, stood at an intersection with classmates and waved signs in protest — hopeful his efforts might affect change.

That same month, the Boy Scouts announced a proposed resolution that would end its longtime ban on openly gay youth but not adults, stating “no youth may be denied membership in the Boy Scouts of America on the basis of sexual orientation or preference alone.” At the time, Felker said she had “mixed feelings” about it. “I am thrilled that the Boy Scouts of America has been able to see that gay youth deserve a chance to participate in a Scouting program equal to any person regardless of sexual orientation,” she said. “I’m very disappointed the ban on adult leaders is still in place.”

Then in February last year, Tessier achieved his dream: He walked into a meeting with Boy Scout Troop 52 and walked out an Eagle Scout — a moment he feared he had jeopardized during his demonstration against discrimination.

“It’s just really amazing, and it honestly hasn’t really sunk in yet,” the then 17-year-old told The Post. “We didn’t know if it was going to happen at all.” Though he knew it was temporary. Everything would change when he turned 18.

“It’s kind of a backhanded acceptance: We accept you for now,” he added.

In his open letter last year, Tessier called on former U.S. Defense Secretary Robert Gates, president of Boy Scouts of America, to do for the Boy Scouts what he helped accomplish for the U.S. military — revoking the ban on gay service members.

“It’s a watershed moment,” Wahls said of the New York decision. “This is the first time any Boy Scout council had said it’s employing an openly gay Scout. I think the leadership he exhibited in standing up against the ban on gay youth is the kind of character you want Scouts to learn at camp.”

Wahls then quoted Albus Dumbledore, the fictional headmaster in J. K. Rowling’s “Harry Potter” series: “It takes a great deal of bravery to stand up to your enemies, but a great deal more to stand up to your friends.”

“And,” Wahls added, “Pascal did exactly that.”