In 1994, Steele joined Sun Microsystems and was invited by Bill Joy to become a member of the Java team after the language had been designed, since he had a track record of writing good specifications for existing languages. He was named a Sun Fellow in 2003.
Steele also designed the original command set of Emacs and was the first to port TeX (from WAITS to ITS). He has published papers on other subjects, including compilers, parallel processing, and constraint languages. One song he composed has been published in Communications of the Association for Computing Machinery (CACM) ("The Telnet Song," April 1984, a parody of the behavior of a series of PDP-10  implementations written by Mark Crispin).
Steele has served on accredited standards committees ECMA TC39 (ECMAScript, for which he was editor of the first edition), X3J11 (the C language), and X3J3 (Fortran) and is currently chairman of X3J13 (Common Lisp). He was also a member of the IEEE working group that produced the IEEE Standard for the Scheme Programming Language, IEEE Std 1178-1990. He represents Sun Microsystems in the High Performance Fortran Forum, which produced the High Performance Fortran specification in May, 1993.
In addition to specifications of the Java programming language, Steele's work at Sun Microsystems has included research in parallel algorithms, implementation strategies, and architectural and software support. In 2005, Steele began leading a team of researchers at Sun developing a new programming language named Fortress, a high-performance language designed to obsolete Fortran.
Steele and Samuel P. Harbison wrote C: A Reference Manual, (Prentice-Hall, 1984; ISBN 0-13-110016-5), to provide a precise description of the C programming language, which Tartan Laboratories was trying to implement on a wide range of systems. Both authors participated in the ANSI C standardization process; several revisions of the book were issued to reflect the new standard.
In 1984, Steele published Common Lisp the Language (Digital Press; ISBN 0-932376-41-X; 465 pages). This first edition was the original specification of Common Lisp ("CLtL1") and served as the basis for the ANSI standard. Steele released a greatly expanded second edition in 1990, (Digital Press; ISBN 1-55558-041-6; 1029 pages) which documented a near-final version of the ANSI standard.
Steele, along with Charles H. Koelbel, David B. Loveman, Robert S. Schreiber, and Mary E. Zosel wrote The High Performance Fortran Handbook (MIT Press, 1994; ISBN 0-262-11185-3).