Flory was born at Sterling, Illinois, and educated at Ohio State University, where he obtained his PhD in 1934. His career was divided between industry and university. He worked with Du Pont from 1934 until 1938 on synthetic polymers and then spent the next two years at the University of Cincinnati. After working for Standard Oil from 1940 until 1943, Flory served as Director of Fundamental Research for the Goodyear Tire Company in Akron, Ohio, until 1948. He was then appointed to the chair of chemistry at Cornell. He left Cornell in 1957 to become director of research of the Mellon Institute in Pittsburgh and, finally, in 1961, accepted the chair of chemistry at Stanford University, California.

Flory was one of the people who, in the 1930s, began working on the properties of polymers. A particular problem at the time was that polymer molecules do not have a definite size and structure; a given polymeric material consists of a large number of macromolecules with different chain lengths. Flory approached this problem using statistical methods, obtaining expressions for the distribution of chain lengths.

In further work he developed a theory of nonlinear polymers, which involve cross linkages between molecular chains. He showed how such extended structures can form from a solution of linear polymers. A particular innovation was the concept of Flory temperature – a temperature for a given solution at which meaningful measurements can be made of the properties of the polymer.

In later work Flory considered the elasticity of rubbers and similar polymeric materials. He published two authoritative books: Principles of Polymer Chemistry (1953) and Statistical Mechanics of Chain Molecules (1969). For his major contribution in the field Flory was awarded the Nobel Prize for chemistry in 1974.