Malcolm Muir, 93, former editor-in-chief of Newsweek magazine, died of pneumonia Tuesday at his home in New York City.

He retired from Newsweek in 1961 when it was purchased by The Washington Post but remained as honorary chairman of the board until 1970. He had been with the magazine since 1937, starting as president and a director of Newsweek, Inc.

Mr. Muir's career in the publishing field started in 1905 with a trade paper that was one of the predecessors of the McGraw-Hill Publishing Co. When that firm was established in 1917, he became vice president and then president until 1937.

From 1967 to 1973, Mr. Muir was chairman of the American advisory council to the Ditchley Foundation in England.The foundation sponsors conferences on Anglo-American relations. He also was chairman of the U.S. Commission for United World Colleges.

Six years ago, Mr. Muir, who was of Scottish ancestry, was made a knight commander of the Order of the British Empire.

He was born in Glen Ridge, N.J, and was educated in private and public schools.

In the early part of the New Deal, he served as a divisional administrator of the National Recovery Administration. Later he was on the board of directors of the American Arbitration Association and the Foreign Policy Association.

He was a member of the International Chamber of Commerce, the Burns Society, the St. Andrew's Society, the St. George's Society and the Pilgrims of the United States.

He is survived by his wife, Frnaces Tener Muir, of the home; a son, Malcolm Jr., of New York City; a daughter, Eleanor Muir Johnson, of Far Hills, N.J, seven grandchildren and 10 great-grandchildren.