Dr. Steitz earned her BS in chemistry from Antioch College in 1963. Significant findings from her work emerged as early as 1967, when her Harvard PhD thesis with Jim Watson examined the test-tube assembly of a ribonucleic acid (RNA) bacteriophage (antibacterial virus) known as R17.

Steitz spent the next three years in postdoctoral studies at the Medical Research Council Laboratory of Molecular Biology in Cambridge, England, where she used early methods for determining the biochemical sequence of RNA to study how ribosomes know where to initiate protein synthesis on bacterial mRNAs. In 1970, she was appointed assistant professor of molecular biophysics and biochemistry at Yale, becoming full professor in 1978. At Yale, she established a laboratory dedicated to the study of RNA structure and function. In 1979, Steitz and her colleagues described a group of cellular particles called small nuclear ribonucleoproteins, a breakthrough in understanding how RNA is spliced.

Steitz is an investigator with the Howard Hughes Medical Institute, a member of the American Academy of Arts and Sciences, the American Philosophical Society, the National Academy of Sciences, and the Institute of Medicine. Her many honors include the National Medal of Science (1986), the FASEB Excellence in Science Award (2003), the RNA Society Lifetime Achievement Award (2004), the Howard Taylor Ricketts Award (2004), E.B. Wilson Medal (2005), Rosalind E. Franklin Award for Women in Science from the National Cancer Institute (2006). She is the recipient of 11 honorary degrees.