Ralph Brewster graduated from Bowdoin College with the A. B. in 1909. After serving as a high school principal for one year, Brewster enrolled in Harvard Law School, where he earned money by waiting on tables and tutoring other students.
He receiving the LL. B. from Harvard in 1913.
After receiving his LL. B Brewster began practicing law in Portland, Maine.
In Portland he soon entered Republican party politics, winning election to the lower house of the Maine legislature in 1916. In 1918 he resigned to enter the army. When the armistice was signed, Brewster was in the officers' candidate school at Camp Zachary Taylor, Kentucky. He was reelected to the Maine House of Representatives that year, and in 1922 he was elected to the Maine Senate.
Brewster was elected for the first time as a governor of Maine in 1924 and then in 1926. After his second term as governor, Brewster returned to private law practice. Over the next few years he suffered successive political setbacks. Twice he was defeated for the Republican nomination as candidate for the United States Senate. He then moved from Portland to Dexter, hoping to win a seat in Congress from Maine's Third District.
In 1932 he lost a close congressional election to Democrat John G. Utterback, but in 1934 he defeated Utterback, partly because of his support for the Townsend Pension Plan, which was popular in Maine. Brewster's three terms in the House and his later career in the Senate were stormy. He opposed most of Franklin D. Roosevelt's New Deal, particularly the Supreme Court "packing" plan and the bill to abolish public-utility holding companies. The latter bill embroiled him in a controversy with Thomas G. Corcoran, one of the president's advisers. Brewster accused Corcoran of threatening to stop construction on the Passamaquoddy Bay tidal power project in Maine unless Brewster voted for the "death sentence clause" of the public-utility holding company act. Corcoran vigorously denied the charges. Subsequently the "Quoddy" project was abandoned.
He became a member of the Senate Naval Affairs Committee, and after American entry into World War II, he was named to the War Investigating Committee, headed by Harry Truman. He was one of five committee members who made a world tour in 1943 to study military installations and lend-lease administration. Despite partisan differences, Brewster and Truman became close friends.
Brewster also served on the Joint Congressional Committee of Inquiry formed in 1946 to investigate the attack on Pearl Harbor. The majority report placed the blame for this disaster solely on the military in Hawaii and Washington.
In August 1947, Brewster, as chairman of the Senate War Investigating Committee, launched a subcommittee investigation into the $40 million in contracts awarded to the Hughes Aircraft Company during the war. Howard Hughes charged that Brewster had attempted to "blackmail" him into merging his Trans World Airlines with Pan American Airways by offering to quash the inquiry. In an unprecedented move, Brewster appeared as a witness before his own committee and denied the accusation under oath. The inquiry eventually came to nothing.
In 1952, Brewster testified before the House Ways and Means Committee concerning a $10, 000 check he had given in 1950 to Henry W. Grunewald, a one-time Washington influence peddler. Denying any wrongdoing, he testified that the money was designated for the primary campaigns of Senator Milton R. Young of North Dakota and Richard M. Nixon of California. (Nixon was running for the Senate for the first time. )
As chairman of the Republican Senate Campaign Committee, Brewster stated, he could not openly contribute, so he had used Grunewald as a "conduit" to transfer the money to the two candidates as a loan. Brewster became a member of the Senate Foreign Relations Committee in 1951.
The following year, in his bid for reelection, he lost the primary to Governor Frederick G. Payne in a campaign focusing on a liquor scandal in which both candidates were accused of graft. Both denied the charges. In retirement Brewster played an active role in Americans for Constitutional Action, a conservative organization.
Brewster died unexpectedly of cancer on Christmas Day, 1961 in Brookline, Massachusetts.
He was buried at Mount Pleasant Cemetery in Dexter, Maine where his home, which is listed on the National Register of Historic Places, was converted to the Brewster Inn, a bed and breakfast.
A Christian Scientist, Ralph Brewster was president of the First Church of Christ, Scientist, in Boston in 1932-1933.
In Portland he entered Republican party politics, winning election to the lower house of the Maine legislature in 1916.
His association with McCarthyism eroded Brewster's political support as McCarthy's anti-communist excesses became increasingly unpopular. His earlier association with the Ku Klux Klan had already cost him support in liberal Republican circles.
During his time in Congress, Brewster worked on legislation to provide old-age pensions (the forerunner of Social Security) although he was a prominent opponent of welfare and spending programs in President Roosevelt's New Deal. As Senator, Brewster sat on several committees, notably the Special Senate Committee to Investigate the National Defense Program (the Truman Committee), and the Joint Committee to Investigate the Pearl Harbor attack.
Brewster played a role in defeating the signature New Deal project in his own district of Maine, a multibillion-dollar tidal power development planned for Passamaquoddy Bay. Supported by President Roosevelt, whose summer home on Campobello was within sight of the project area, Brewster initially seemed to be an ally.
Brewster was a member of the Christian Science Society in Dexter, Maine. He was also a member of the American Bar Association, Grange, the American Legion, the Freemasons, the Elks, the Odd Fellows, and Delta Kappa Epsilon.
On April 20, 1915, he married Dorothy Foss; they had two sons.