Walter Brattain was born in Xiamen, Fujian, China, to American parents Ross R. Brattain and Ottilie Houser Brattain. Ross R. Brattain was a Teacher at the Ting-Wen Institute, a private school for Chinese boys. Both parents were graduates of Whitman College; Ottilie Houser Brattain was a gifted Mathematician. Ottilie and baby Walter returned to the United States in 1903, followed by Ross. The family lived for several years in Spokane, Washington, then settled on a cattle ranch near Tonasket, Washington in 1911.

Brattain attended high school in Washington, spending one year at Queen Anne High School in Seattle, two years at Tonasket High School, and one year at Moran School for Boys on Bainbridge Island. Brattain then attended Whitman College in Walla Walla, Washington, where he studied with Benjamin H. Brown (physics) and Walter A. Bratton (mathematics). Brattain earned a bachelor's degree from Whitman College in 1924, with a double major in physics and mathematics. Brattain and his classmates Walker Bleakney, Vladimir Rojansky and E. John Workman were later known as "the four horsemen of physics" because all went on to distinguished careers. Brattain's brother Robert, who followed him at Whitman College, also became a Physicist.

Brattain earned a Master of Arts from the University of Oregon in Eugene in 1926, and a Ph.D. from the University of Minnesota in 1929. At Minnesota, Brattain had the opportunity to study the new field of quantum mechanics under John Hasbrouck Van Vleck. His thesis, supervised by John T. Tate, was Efficiency of Excitation by Electron Impact and Anomalous Scattering in Mercury Vapor.

From 1927 to 1928 Brattain worked for the National Bureau of Standards in Washington, D.C., where he helped to develop piezoelectric frequency standards. In August 1929 he joined Joseph A. Becker at Bell Telephone Laboratories as a research Physicist. The two men worked on the heat-induced flow of charge carriers in copper oxide rectifiers. Brattain was able to attend a lecture by Arnold Sommerfeld. Some of their subsequent experiments on thermionic emission provided experimental validation for the Sommerfeld theory. They also did work on the surface state and work function of tungsten and the adsorption of thorium atoms. Through his studies of rectification and photo-effects on the semiconductor surfaces of cuprous oxide and silicon, Brattain discovered the photo-effect at the free surface of a semiconductor. This work was considered by the Nobel prize committee to be one of his chief contributions to solid state physics.

At the time, the telephone industry was heavily dependent on the use of vacuum tubes to control electron flow and amplify current. Vacuum tubes were neither reliable nor efficient, and Bell Laboratories wanted to develop an alternative Technology. As early as the 1930s Brattain worked with william B. Shockley on the idea of a semiconductor amplifier that used copper oxide, an early and unsuccessful attempt at creating a field effect transistor. Other researchers at Bell and elsewhere were also experimenting with semiconductors, using materials such as germanium and silicon, but the pre-war research effort was somewhat haphazard and lacked strong theoretical grounding.

During World War II, both Brattain and Shockley were separately involved in research on magnetic detection of submarines with the National Defense Research Committee at Columbia University. Brattain's group developed magnetometers sensitive enough to detect anomalies in the earth's magnetic field caused by submarines. As a result of this work, in 1944, Brattain patented a design for a magnetometer head.

In 1945, Bell Labs reorganized and created a group specifically to do fundamental research in solid state physics, relating to communications technologies. Creation of the sub-department was authorized by the vice-president for research, Mervin Kelly. An interdisciplinary group, it was co-led by Shockley and Stanley O. Morgan. The new group was soon joined by John Bardeen. Bardeen was a close friend of Brattain's brother Robert, who had introduced John and Walter in the 1930s. They often played bridge and golf together. Bardeen was a quantum Physicist, Brattain a gifted experimenter in materials science, and Shockley, the leader of their team, was an expert in solid-state physics.

Convinced by the 1947 demonstration that a major breakthrough was being made, Bell Laboratories focused intensively on what it now called the Surface States Project. Initially, strict secrecy was observed. Carefully restricted internal conferences within Bell Labs shared information about the work of Brattain, Bardeen, Shockley and others who were engaged in related research. Patents were registered, recording the invention of the point-contact transistor by Bardeen and Brattain. There was considerable anxiety over whether Ralph Bray and Seymour Benzer, studying resistance in germanium at Purdue University, might make a similar discovery and publish before Bell Laboratories.

Brattain transferred to another research group within Bell Laboratories, working with C. G. B. Garrett, and P. J. Boddy. He continued to study the surface properties of solids and the "transistor effect", so as to better understand the various factors underlying semiconductor behavior. Describing it as "an intolerable situation", Bardeen left Bell Laboratories in 1951 to go to the University of Illinois, where he eventually won a second Nobel Prize for his theory of Superconductivity. Shockley left Bell Laboratories in 1953 and went on to form the Shockley Semiconductor Laboratory at Beckman Instruments.

Brattain taught at Harvard University as a visiting lecturer in 1952 and at Whitman College as a visiting lecturer in 1962 and 1963, and a visiting professor beginning in 1963. Upon formally retiring from Bell Laboratories in 1967, he continued to teach at Whitman, becoming an adjunct professor in 1972. He retired from teaching in 1976 but continued to be a consultant at Whitman.

In 1956, the three men were jointly awarded the Nobel Prize in Physics by King Gustaf VI Adolf of Sweden "for research on semiconductors and the discovery of the transistor effect." Bardeen and Brattain were included for the discovery of the point-contact transistor; Shockley for the development of the junction transistor. Walter Brattain is credited as having said, when told of the award, "I certainly appreciate the honor. It is a great satisfaction to have done something in life and to have been recognized for it in this way. However, much of my good fortune comes from being in the right place, at the right time, and having the right sort of people to work with." Each of the three gave a lecture. Brattain spoke on Surface Properties of Semiconductors, Bardeen on Semiconductor Research Leading to the Point Contact Transistor, and Shockley on Transistor Technology Evokes New Physics.

Walter Brattain married twice. His first wife was Chemist Keren Gilmore. They married in 1935 and had a son, william G. Brattain, in 1943. Keren Gilmore Brattain died April 10, 1957. Walter Brattain married Mrs. Emma Jane (Kirsch) Miller, who already had three children, in 1958.

He moved to Seattle, Washington, in the 1970s where he lived until his death. He died on October 13, 1987, in a nursing home in Seattle from Alzheimer's Disease. He is buried in Pomeroy City Cemetery, Garfield County, Washington, USA.