Garner has been editor in chief of Black's Law Dictionary since its seventh edition. After graduating from the University of Texas School of Law, he clerked for Judge Thomas M. Reavley of the U.S. Court of Appeals for the Fifth Circuit, then practiced at a major firm in Dallas. He then began teaching, first at his alma mater and now at Southern Methodist University School of Law.

As an undergraduate, Garner studied linguistics and the English classics at the University of Texas and Oxford. At the University of Texas School of Law, he served as associate editor of the Texas Law Review and began writing A Dictionary of Modern Legal Usage.

Garner has authored many publications. His works include The Elements of Legal Style, The Winning Brief, Legal Writing in Plain English, Securities Disclosure in Plain English, and many other books and articles. In 2003, The Chicago Manual of Style incorporated his restatement of English grammar into its 15th edition.

Garner has been a member of the American Law Institute since 1992, serving as lead reviser on its committee on bylaws and council rules. From 1992 to 1999, he helped restyle federal rules for the U.S. Judicial Conference's Standing Committee on Rules of Practice and Procedure. He has restyled rules for courts in other states as well, including California and Texas. The Association of Reporters of Judicial Decisions recognized his contributions to judicial writing in 1994 with the prestigious Henry C. Lind Award, and in 2005 the Plain Language Institute presented him its Lifetime Achievement Award.