Rear Adm. Kevin M. Sweeney has resigned his post as chief of staff to the United States secretary of defense, the Defense Department said Saturday.
Mr. Sweeney had become chief of staff to former Defense Secretary Jim Mattis in January 2017, and his resignation comes soon after Mr. Mattis’s own pointed departure in December. The two had known each other for years.
Mr. Mattis said then that he had resigned in protest of President Trump’s decision to withdraw American forces from Syria and in protest of the president’s rejection of international alliances.
Mr. Mattis had originally said he would step down at the end of February, but angered by Mr. Mattis’s criticism, Mr. Trump said he was removing Mr. Mattis from his post two months early.
Patrick M. Shanahan, the former deputy secretary of defense, replaced Mr. Mattis and became acting secretary of defense on Jan. 1.
“After two years in the Pentagon, I’ve decided the time is right to return to the private sector,” Mr. Sweeney said in a statement on the department’s website. “It has been an honor to serve again alongside the men and women of the Department of Defense.”
A spokeswoman for the department said Saturday that she did not have any further comment beyond the statement. Mr. Sweeney could not immediately be reached for comment.
Mr. Sweeney retired as a rear admiral from the United States Navy in 2014, according to the Department of Defense. The department said as commanding officer of the U.S.S. Cole, he had overseen the destroyer’s restoration.
He had also served as executive assistant to the under secretary of the Navy and executive assistant to the commander of the Joint Forces Command.
After his retirement from active duty, Mr. Sweeney spent time working in various executive roles in the private sector, according to the Defense Department. He graduated from the Naval Academy in 1982.
Mr. Sweeney’s resignation follows a number of recent high-profile departures from the Trump administration, including that of Mr. Mattis. The president said in December that John F. Kelly would step down as White House chief of staff. Brett McGurk, the special presidential envoy to the coalition fighting the Islamic State, also announced his resignation last month.