Park was born in Harveyville, Pennsylvania, and grew up in Minnesota. He was educated at the University of Michigan, where he was taught by the pragmatist philosopher John Dewey. His concern for social issues, and especially issues related to race in the cities, led him to become a journalist in Chicago.

After being a journalist in various U.S. towns 1887 - 1898, he then studied Psychology and Philosophy for an MA at Harvard 1898-9, being taught by another prominent pragmatist philosopher, William James. After graduation, he went to Germany, studying in Berlin, Straßburg (today Strasbourg, France) and Heidelberg between 1899 and 1903, before returning to the United States. He studied philosophy and sociology in 1899 - 1900 with Georg Simmel at Berlin, spent a semester in Straßburg 1900, and took his PhD in Philosophy in 1903 at Heidelberg under Wilhelm Windelband (1848 - 1915) and Alfred Hettner (1859 - 1941); Dissertation: Masse und Publikum. Eine methodologische und soziologische Untersuchung. He returned to the U.S. in 1903, briefly becoming an assistant in philosophy at Harvard 1904-5.

Park taught at Harvard, until Booker T. Washington invited him to the Tuskegee Institute to work on racial issues in the southern U.S. He joined the Department of Sociology at the University of Chicago in 1914, staying there until his retirement in 1936. He continued teaching until his death, however, at Fisk University. Park died in Nashville, Tennessee, at the age of seventy-nine.

"The marginal man ... is one whom fate has condemned to live in two societies and in two, not merely different but antagonistic cultures .... his mind is the crucible in which two different and refractory cultures may be said to melt and, either wholly or in part, fuse." [Robert E. Park, 1937]

During his lifetime Park became a well-known figure both within and outside the academic world. At various times from 1925 he was president of the American Sociological Association and of the Chicago Urban League, and was a member of the Social Science Research Council.

"Go and sit in the lounges of luxury hotels and on the doorsteps of the flophouses; sit on the Gold Coast settees and on the slum shakedowns; sit in the Orchestra Hall and in the Star and Garter Burlesque. In short go and get the seat of your pants dirty in real research." [Robert Park, 1927]

Park was influential in developing the theory of assimilation as it pertained to immigrants in the United States. He argued that there were four steps to the Race Relations Cycle in the story of the immigrant. The first step was contact then followed by competition. In the third step each group would accommodate each other. Finally, when this failed, the immigrant group would learn to assimilate. "Park probably contributed more ideas for analysis of racial relations and cultural contacts than any other modern social scientist." What is more important, this theory of four steps (or four levels), according to its author, may be applied not only to immigration, but also to all other dynamic social processes.

During Park's time at the University of Chicago, its sociology department began to use the city that surrounded it as a sort of research laboratory. His work – together with that of his Chicago colleagues, such as Ernest Burgess, Homer Hoyt, and Louis Wirth – developed into an approach to urban sociology that became known as the Chicago School: "I have been mainly an explorer in three fields: Collective Behavior; Human Ecology; and Race Relations."

"At the University of Chicago, where American sociology became involved more with people than with methodology, Robert Ezra Park developed the idea of a marginal personality (Park & Burgess, 1921). He postulated that the loyalties that bind persons together in primitive societies are in direct proportion to the intensity of the fears and hatreds with which they view other societies. This concept is developed as theories of ethnocentrism and in-group/out-group propensities. Group solidarity correlates to a great extent with animosity toward an out-group." (Billie Davis, Marginality in a Pluralistic Society)

Park's introduction of the term ecology into sociology came via inspiration from one of the founders of ecology, the botanist Eugen Warming, but also from geographers such as J. Paul Goode who developed a first version of human ecology before World War I.