While at IBM, John W. Backus proposed an alternative to assembly language for programming the IBM 704 mainframe computer in 1953. A draft specification for The IBM Mathematical Formula Translating System was completed mid-1954. The first optimizing FORTRAN compiler was delivered in April 1957.

The language was extremely efficient and widely adopted for writing numerically intensive programs. The inclusion of complex number data types in the language made Fortran especially suited to technical applications such as engineering and scientific simulation. It also provided a solution to two primary problems in computing at that time: making programming easier for humans and providing a structured higher level framework for the creation of mathematical solutions to algebraic systems. It is in use in high performance computing (HPC) to this day.

He worked closely with Peter Naur (see also), from Denmark, to develop a system for describing programming languages. It is now known as Backus-Naur form (BNF).

He had an informal style and an aptitude for problem solving skills. He was one of the hackers of his day.