WASHINGTON — Former Defense Secretary Mark Esper has dropped a lawsuit against the Defense Department in which he claimed that material was being improperly withheld from his use as he wrote a memoir about his tenure in the Trump administration.

Esper’s lawyer, Mark S. Zaid, said in a statement on Friday that the Pentagon had reversed its stance on “the overwhelming majority” of material that officials had deemed classified and thus not for publication. What remained in dispute over its classification wasn’t central to Esper’s book, Zaid said.

The lawsuit filed Nov. 28 in U.S. District Court in Washington contended that “significant text” in the memoir was being improperly held under the guise of classification. Esper has said publicly that some 60 pages of the manuscript contained redactions at one point during a security review and maintained that no classified information was being used.

The book, “A Sacred Oath,” will be published in May, Zaid said.

The book covers Esper’s time as Army secretary, 2017 to 2019, and his 18 months as defense secretary. President Donald Trump fired the West Point graduate and Gulf War veteran in a tweet shortly after Trump lost his reelection bid.

Esper and Trump clashed over several issues while Esper led the Pentagon, including the use of the military during civil unrest in June 2020 following the killing of George Floyd. No other president had fired a defense secretary after losing an election; doing so allowed Trump to place loyalists in leading Pentagon positions as he disputed his loss to Democrat Joe Biden.

The lawsuit described the period in which Esper was Pentagon chief as “an unprecedented time of civil unrest, public health crises, growing threats abroad, Pentagon transformation, and a White House seemingly bent on circumventing the Constitution.”