From a young age, maritime and shipping lawyer Mark P. Schlefer liked to challenge authority.

Why, he asked as a child, did he have to stand for the Pledge of Allegiance at his elementary school on the Upper West Side of Manhattan? Why, he asked at 22, wasn’t he allowed inside an officers’ club in France for a glass of champagne to toast Germany’s surrender at the end of World War II, especially after surviving 36 combat missions as a bombardier-navigator? Why, he asked a few years later as a young father, was it that the Washington-area private schools attended by his children largely excluded Black students?

His willingness to ask questions of people in power carried over to his professional life and led to his role in the development of the Freedom of Information Act, the landmark legislation providing citizens with a tool to keep the government open and honest.

Mr. Schlefer, a former Washington resident, died Nov. 2 at his home in Putney, Vt. The cause was cardiorespiratory arrest, said a daughter, Katharine Schlefer Dodge. He was 98.

In the early 1960s, while practicing law, Mr. Schlefer questioned why his client, the shipping company Pacific Far East Line, was denied permission from the U.S. Maritime Commission to conduct business in the Mariana Islands, a U.S. territory in the Pacific Ocean. He was frustrated when the commission told him its reasoning was confidential.

He scheduled a meeting with the American Bar Association to suggest the drafting of a bill to gain access to government documents. He soon joined two lawyers affiliated with the ABA who had already begun working on such a bill and, together, they drafted the original version of the Freedom of Information Act, or FOIA, Mr. Schlefer recounted in a 2016 Washington Post opinion column.

After the bill won the ABA’s endorsement at its convention in Chicago, Mr. Schlefer met with Rep. John Moss (D-Calif.), who had been campaigning against government secrecy for more than a decade.

“I had planned just to leave [the draft of the bill] with him, but he asked me to sit,” Mr. Schlefer wrote in The Post. “After reading it slowly and carefully, he looked up and said, ‘Mr. Schlefer, I’ll deliver the House. You deliver the Senate.’ ”

Through a well-connected friend, Mr. Schlefer eventually persuaded Senate Judiciary Committee Chairman James Eastland (D-Miss.) to hold a hearing on FOIA legislation.

Moss remained the driving force of the FOIA legislation through Congress as it underwent revisions giving courts power to exempt certain internal agency documents related to executive privilege, national security, personnel records and criminal investigations.

President Lyndon B. Johnson signed the Freedom of Information Act into law on July 4, 1966. It has been amended several times since and remains a primary and often-used tool for making government decision-making open to public view, Mr. Schlefer wrote.

Mark Pascal Schlefer was born in Manhattan on May 9, 1922, to stockbroker parents. He graduated from Harvard University in 1943 and its law school in 1949. Between degrees, he served in the Army Air Forces in Europe during World War II. (He had been turned away from an officers’ club — despite holding the rank of lieutenant — by an unpleasant sergeant, but Mr. Schlefer appealed successfully to a serviceman of higher rank.)

Mr. Schlefer moved to Washington in 1951 and appeared to be in line for a legal position at the State Department, but the job never materialized. He learned later that his application had been flagged as a problem because his wife’s aunt, Carol Weiss King, was a prominent immigration lawyer who had represented left-wing radicals threatened with deportation.

He spent most of his career with the law firm Radner, Zito, Kominers & Fort, which later became Fort & Schlefer.

His wife of 70 years, the former Marion King, died in 2015. In addition to his daughter, of Putney, survivors include two other children, Jonathan Schlefer of Boston and Ellen Schlefer of Durham, N.H.; five grandchildren; and two great-grandchildren.

In 1963, after Mr. Schlefer grew distressed about the lack of racial diversity among students at his children’s private schools, he co-founded what is now the Black Student Fund to provide tuition assistance for minority families at Washington-area private schools.

He also served as board chairman of the Lawyers Alliance for World Security, which lobbies for nuclear arms control. He moved to Putney from Washington in 2005 and retired from law practice two years later.

His most enduring contribution to the law remained the FOIA legislation.

“Those of us who drafted the legislation and worked to obtain its enactment never expected the statute to have the long-term importance that it has achieved,” Mr. Schlefer wrote in his self-published biography, “Incidents in a Life: The War is Over, I’d Like a Glass of Champagne.” “We had a local problem, and we sought to fix it. In fact, we ended by fixing a crucial national problem.”