Born in Martinsburg, West Virginia, Baker established a legal practice in Cleveland after graduating from Washington and Lee University School of Law.

He selected General John J. Pershing to command the American Expeditionary Forces, which he insisted act as an independent unit.

He served as an attorney in Village of Euclid v. Ambler Realty Co., a landmark case that established the constitutionality of zoning laws.

In 1892, Baker graduated with bachelor's degree from Johns Hopkins University, where he was a member of Phi Gamma Delta fraternity.

He helped the Democratic candidate Tom L. Johnson to become the mayor of Cleveland, and under his mentorship started his own public career.

[10] When Baker worked on Wilson's behalf at the Democratic National Convention in Baltimore in 1912, he was considered as a possible vice-presidential contender.

Though offered the post twice, Baker declined to serve as United States Secretary of the Interior during President Wilson's first term.

A 1993 survey of historians, political scientists and urban experts conducted by Melvin G. Holli of the University of Illinois at Chicago ranked Baker as the eigteenth-best American big-city mayor to have served between the years 1820 and 1993.

The post also required legal expertise because of the War Department's role in administering the Philippines, the Panama Canal, and Puerto Rico.

... On the day President Woodrow Wilson announced Baker's appointment as secretary of war, he admitted his ignorance of military matters.

At one meeting with British Prime Minister, David Lloyd George, Baker told him that "if we want advice as to who should command our armies, we would ask for it.

"[citation needed] On December 15, 1917, a War Council was formed (as distinct from the Council of National Defense) consisting of the Secretary of War, his Assistant, the Chief of Staff of the United States Army, the Quartermaster General of the United States Army, the Chief of Ordnance and possibly others.

[14] The War Council was to oversee and coordinate all matters of supply and to plan for the effective use of the military power of the nation.

Problems began quickly to crop up and on 18 December, three days after its formation, Baker fired three of the five officers appointed to the War Council.

... And I swore an obligation to the dead that in season and out, by day and by night, in church, in political meeting, in the market-place, I intended to lift up my voice always and ever until their sacrifice were really perfected.

[20] According to a New York Times editorial, For a moment that vast audience was lifted from partisan thoughts to heights from which it could have a glimpse of the promised land of peace.

"[22] In 1928, President Coolidge appointed Baker a member of the Permanent Court of Arbitration of The Hague, and he was reappointed to another six-year term by Roosevelt in 1935.

[23][24] In 1929, President Herbert Hoover appointed Baker to the Wickersham Commission on issues relating to law enforcement, criminal activity, police brutality, and Prohibition.

[26] Baker argued before the U.S. Supreme Court as counsel for the property owner in Village of Euclid v. Ambler Realty Co., a landmark case that established the constitutionality of zoning laws.

[27] Baker served on the Board of Trustees of Johns Hopkins University beginning in 1918 and was considered for appointment as president of the institution in 1928.

[32][16] After lying in state with full military honors at Trinity Cathedral and a simple funeral at the family's request, Baker was buried in Lake View Cemetery.

[33] During World War II the Liberty ship SS Newton D. Baker was built in Panama City, Florida, and named in his honor.

Located on the corner of Adelbert and Euclid, across from Severance Hall, it served as a large unit of general purpose classrooms and administrative offices.

A dormitory at Ohio State University, dedicated in 1940, is named Baker Hall (see information about the building) Archived December 16, 2016, at the Wayback Machine in his honor.