A top advisor to Defense Secretary Pete Hegseth has left the Pentagon after six months of service, the Department of Defense (DoD) confirmed to Fox News Digital on Saturday.

Justin Fulcher told Fox News Digital he formally resigned on Thursday evening, describing the decision as entirely his own.

Fulcher said he had originally planned to serve six months in government and, having reached that point, chose to move on “amicably.” He also emphasized what he described as the “great work” being done by Hegseth “for our troops and country.”

“The Department of Defense is grateful to Justin Fulcher for his work on behalf of President [Donald] Trump and Secretary Hegseth. We wish him well in his future endeavors,” chief Pentagon spokesman Sean Parnell said in a statement.

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Fulcher tells Fox News Digital that he resigned voluntarily on Thursday evening amicably from SecDef Hegseth’s Pentagon staff. (Omar Havana/Getty Images)

In addition to advising Hegseth on personnel and policy, Fulcher played a role in several defense initiatives during his tenure, he told Fox News Digital.

Fulcher said he contributed to reviews of major acquisition programs aimed at strengthening lethality and the U.S. industrial base, and helped streamline software procurement timelines “from years to months,” modernizing key IT systems across the department.

He also said he supported Hegseth in high-level meetings across the Indo-Pacific, including the Shangri-La Dialogue in Singapore, and participated in efforts that redirected nearly $50 billion from non-lethal line items into readiness and more impactful defense programs.

Fulcher praised the “dedicated men and women of the Department of Defense,” cited progress in “revitalizing the warrior ethos” and “rebuilding the military,” and thanked both Hegseth and Trump for their leadership. “Still, this is just the beginning,” Fulcher added.

Fulcher, who had served as a senior advisor to Hegseth since April, announced his departure Saturday afternoon in a message posted to X. 

“As planned, I’ve completed 6 months of service in government to my country,” he wrote, calling the experience “incredibly inspiring.”

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Justin Fulcher in an undated photo. Fulcher, a senior advisor to Defense Secretary Pete Hegseth, exited the Pentagon on Thursday after completing six months in the role. (Courtesy @JustinFulcher via X)

“None of this could have happened without Secretary Hegseth’s decisive leadership or President Trump’s continued confidence in our team,” he wrote. “I will continue to champion American warfighters in all future endeavors.”

Fulcher joined the DoD earlier this year as part of Hegseth’s inner circle, a cohort of loyal advisers appointed after Hegseth took the helm at the Pentagon in Trump’s second term.

Fulcher had served six months at the Pentagon before confirming his resignation on Thursday night with Fox News Digital. (J. David Ake/Getty Images)

His departure comes amid a broader reshuffling of senior personnel inside Hegseth’s office. At least six aides have left since January, though defense officials have downplayed the moves as standard transitions.

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It’s unclear what Fulcher’s next step will be, though his statement suggests he intends to remain active in national security circles.

The Pentagon has not yet named a replacement.