In 1942, he was commissioned to write a history of United States naval operations in World War II, which was published in 15 volumes between 1947 and 1962.

He was named for his maternal grandfather Samuel Eliot—a historian, educator, and public-minded citizen of Boston and Hartford, Connecticut.

Morison attended Noble and Greenough School (1897–1901) and St. Paul's (1901–1903) prior to entering Harvard University, where he was a member of the Phoenix S K Club.

Morison originally intended to major in mathematics until Albert Bushnell Hart talked him into researching some papers of an ancestor stored in his wine cellar.

[4] His Harvard dissertation was the basis for his first book The Life and Letters of Harrison Gray Otis, Federalist, 1765–1848 (1913), which sold 700 copies.

In 1940, Morison published Portuguese Voyages to America in the Fifteenth Century, a book that presaged his succeeding publications on the explorer, Christopher Columbus.

The Harvard Columbus Expedition, led by Morison and including his wife and Captain John W. McElroy, Herbert F. Hossmer, Jr., Richard S. Colley, Dr. Clifton W. Anderson, Kenneth R. Spear and Richard Spear, left on 28 August 1939 aboard the 147 foot ketch Capitana for the Azores and Lisbon, Portugal from which they sailed on the 45 foot ketch Mary Otis to retrace Columbus' route using manuscripts and records of his voyages reaching Trinidad by way of Cadiz, Madeira, and the Canary Islands.

[2] Gregory Pfitzer explained his procedures:[9] He gained berths on patrol boats, destroyers, and heavy cruisers; participated in planning sessions for invasions; witnessed sea battles; narrowly escaped death at the hands of a kamikaze pilot; and conducted post-operational interviews with commanders in the Pacific theater.Morison worked with a team of researchers to prepare the History of United States Naval Operations in World War II, published in 15 volumes between 1947 and 1962, documenting everything from strategy and tactics to technology and the exploits of individuals.

On August 1, 1951, he was transferred to the Honorary Retired List of the Naval Reserve and was promoted to rear admiral on the basis of combat awards.

In the early 1960s, Morison's focus returned to his New England youth, writing The Story of Mount Desert Island, Maine (1960), One Boy's Boston, 1887–1901 (1962), Introduction to Whaler Out of New Bedford (1962), and A History of the Constitution of Massachusetts (1963).

In presenting the distinguished historian with the highest civilian award in the United States, Johnson noted:[11] Scholar and sailor, this amphibious historian has combined a life of action and literary craftsmanship to lead two generations of Americans on countless voyages of discovery.Morison's later years were devoted to books on exploration, such as The Caribbean as Columbus Saw It, written jointly with Mauricio Obregón (1964), Spring Tides (1965), The European Discovery of America (1971–1974), and Samuel de Champlain: Father of New France (1972).

Morison's last known public appearance was on April 8, 1976, when he served as the ribbon cutter to open the USS Constitution Museum.

First published in 1930, the first two editions of the textbook, according to these critics, echoed the thesis of American Negro Slavery (1918) by Ulrich Bonnell Phillips.

[20] In 1950, despite denying any racist intent (he noted his daughter's marriage to the son of Joel Elias Spingarn, the second president of the NAACP), Morison reluctantly agreed to most of the demanded changes.

[21] Morison refused to eliminate references to slaves who were loyal and devoted to their masters because they were treated well and to some positive "civilizing" effects of the American system of slavery.

Morison also refused to remove references to stereotypes of African Americans that he believed were vital in accurately depicting the racist nature of American culture in the 19th and the early 20th centuries, an era during which even the most enlightened progressive thinkers routinely explained many aspects of human behavior as a result of innate racial or ethnic characteristics.

On October 21, 2014, the US Navy issued a letter of apology to the last surviving member of the RAAF Hudson crew, which had sighted and duly reported the approach of the Japanese Naval Task Force.

"[23] Award ribbons Other honors Honorary degrees Literary prizes Memorial A statue of Morison sits on the Commonwealth Avenue Mall in Boston.