Secretary of Defense Ash Carter announced an end to the military’s longstanding ban on openly transgender service members on Thursday, fulfilling a key piece of the Obama administration’s historic legacy on LGBT rights.

The move, which will take a year to fully implement, will undoubtedly have an enormous impact on the armed services as a whole and especially on the thousands of transgender troops currently serving in silence. But it will also mark an important — and likely, final — milestone in the remarkable LGBT rights record of the current commander-in-chief.

“This is a capper on his legacy in many ways,” said Kerry Eleveld, Daily Kos writer and author of the book, “Don’t Tell Me To Wait: How the fight for gay rights changed America and transformed Obama’s presidency.”

“I think that LGBT activists going into this presidency had high hopes,” she told NBC News. “And looking back, they will find that even more was accomplished than they imagined could be accomplished.”

President Obama’s historic steps — or in some cases, shoves — toward fuller LGBT equality in America have been well-documented, ranging from symbolic nods of approval to concrete and transformative policy prescriptions. In 2009, he signed into law the first federal protections based on gender identity or sexual orientation with the Matthew Shepard and James Byrd, Jr. Hate Crimes Prevention Act. A year later, he enacted a measure repealing the military’s ban on openly gay service members, known as "don’t ask, don’t tell."

Related: Pentagon Lifts Ban on Transgender Service Members Serving Openly

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What followed, according to Eleveld, was a “domino effect of advancements,” including (but not limited to) his administration’s abandonment of the now-defunct Defense of Marriage Act, which excluded married same-sex couples from federal benefits; an executive order barring federal contractors from discriminating on the basis of sexual orientation or gender identity; the legalization of marriage equality across the country; and, now, his Justice Department’s zero-tolerance approach to “state-sponsored discrimination against transgender individuals.”

The ultimate LGBT equality to-do list is not yet complete; passing federal nondiscrimination protections, for example, remains outstanding. But short of a miracle in Congress that would somehow compel enough of its members to take up the Equality Act, ending the military’s ban on transgender troops will likely be the last major accomplishment of Obama’s LGBT rights record -- one that, by virtually all accounts, has been a rousing success.

“The Obama administration will go down in history as one of the most significant for LGBT Americans,” said Sue Fulton, president of the LGBT military group SPARTA. “I think it’s impossible to understate the impact that this administration has had.”

The foundation of Obama’s last act for equality was laid almost a full year ago, when Defense Secretary Carter announced that the services had six months to figure out the logistics of integrating transgender troops into the military.

Unlike "don't ask, don't tell," which required congressional approval both to become law and to be repealed, the transgender policy was never a statutory bar; that meant that ending it required only the direction of the defense secretary and the president.

As with other pro-LGBT moves from the Obama administration, some advocates grew frustrated with the pace of the change — especially once Carter’s six-month deadline on ending the transgender ban had come and gone without a word.

“It was quite awkward that at an event honoring LGBT Pride month, there was no mention of when or whether the ban on transgender service members will be lifted,” said Aaron Belkin, director of the Palm Center, a think tank that focuses on gender and sexuality in the military, after attending the Defense Department’s LGBT pride ceremony earlier this month. “The Pentagon can only expect more awkward moments if the situation is not resolved soon.”

LGBT advocates are still anxiously awaiting all of the specifics on how the transgender policy will actually change, particularly when it comes to rules governing barracks, sex reassignment surgery, new recruits, and more. Carter said Thursday that the Defense Department had until October to craft and distribute a commanders’ training handbook, medical protocol and guidance for changing a service member’s gender in the Defense Eligibility Enrollment System. That is also the deadline for when all services will be required to provide medically appropriate care and treatment to transgender service members.

But even before the official announcement, many were, nevertheless, elated to hear that changes were indeed on the way.

“While we have been waiting for this ban to end and, yes, it has been frustrating that it has taken so long for the final announcement to be made, without President Obama’s leadership as commander-in-chief, as well as Defense Secretary Carter’s, we wouldn’t even be talking about this,” said Ashley Broadway-Mack, president of the pro-LGBT group American Military Partner Association. “I truly appreciate all of the work [Obama] has done for our community in ending this ban. It’s going to be the last thing of the legacy that he has created to truly have equality within the ranks of our military.”

Others believe the policy change could also go a long way in promoting transgender acceptance outside of the military.

“I think we need more good examples of successful transgender people than just Hollywood actors and actresses,” said former Navy SEAL Kristin Beck, who came out as a trans woman in 2013. “This is going to show that we’re everyday people. We’re in the military, we serve, we’re proud, and we’re patriots.”