The legal thriller is a subgenre of the crime fiction genre, which is rooted in the mystery genre. Like police procedurals, legal thrillers focus on the investigative and legal processes surrounding a crime. However, legal thrillers take it one step further than the police procedural—the narrative continues into the trial and courtroom proceedings. Legal thrillers offer insight into the legal process and the mindsets of those who work within it. Many legal thriller authors have experience working in the legal system as lawyers or judges. Scott Turow was a lawyer when he published Presumed Innocent in 1987 and continued to practice law until 2020. Turow wrote and published several bestsellers alongside his legal career.

Technical detail is a key convention of the legal thriller genre. Presumed Innocent is filled with detailed descriptions of the legal process, such as describing an arraignment or the daily life of a prosecuting attorney, as well as insights into prosecution and defense strategy. His deep first-hand experience with the legal process and justice system in the US gives authenticity to his novels—he offers insider information and insight that enhance the genre.

Like the police procedural, in a legal thriller, the detective is usually a professional investigator, rather than the amateur detective that sometimes features in the mystery genre.