Real-life court cases often come across as the stuff of drama to outsiders. It turns out many insiders find them theatrical, too.

Pamela Wechsler spent nearly 20 years as a state and federal prosecutor and an assistant district attorney for Suffolk and Middlesex counties, but she took time off at points to work as a technical adviser for shows like “Law and Order: Trial by Jury’’ and the film “The Judge,’’ earning some television writing credits along the way. Now Wechsler is on a roll with the recent release of her debut crime thriller, “Mission Hill,’’ the first of a three-book deal, and the announcement that she has signed on to be a writer and co-producer of “Doubt,’’ a new CBS legal mystery series.

While working as a prosecutor, “I was writing without knowing it,’’ says Wechsler, who has a bachelor’s from Tufts University and a law degree from Boston University. “You write openings and closings. You choreograph a little piece of theater.’’

Though that may make it sound as if the transition from the courthouse to screenwriter and novelist was seamless, for the 55-year-old Wechsler, it was a path that required determination, dedication, and plain old grit.

The first big job the Quincy native got after law school was with the Suffolk County district attorney’s office. “Working in the DA’s office was a really sobering experience,’’ says Wechsler, who argued cases against kidnappers, rapists, and murderers in her decade there. On sleepless nights, she says, she didn’t count sheep: She counted victims. And killers.

Wechsler discovered her new vocation when she did a favor for a friend of a friend who was a writer for “The Practice,’’ a television crime show set in Boston. In 2000, while working at the state attorney general’s office, she offered professional advice to make the crime scenes more realistic — and got seriously interested in writing. She tried cases during the day and wrote television scripts at night, teaching herself the craft.

Her career led her to Washington, D.C., where she worked on white-collar cases for the US Department of Justice. She also landed a television agent. In 2004, she happened to be in Los Angeles for a grand jury when she got an offer to work as a legal consultant on “Law and Order: Trial by Jury.’’ She quit her job and moved to Southern California. “In television, when there is a job, you never know how long a show is going to last,’’ she says. “It is not like you can take your time.’’ The show lasted half a season, but she went on to consult at other iterations of the “Law and Order’’ franchise.

In Los Angeles, Wechsler, who is single, had to search hard for an apartment with a doorman and secure parking, a habit she picked up while working homicide. She and her colleagues were rattled by the cold-blooded execution of fellow prosecutor Paul McLaughlin in 1995. “I found one of the few gated apartment complexes out there,’’ she says.

While she enjoyed the consulting work, she yearned to break in as a scriptwriter. She got her chance while working with the husband and wife team of Joan Rater and Tony Phelan. She got her first writing credit for a “Law and Order’’ script about a shaken baby murder, modeled after the Louise Woodward case — the British nanny was convicted of killing an infant in Newton in 1997 — as well as a similar but less well-known case that Wechsler tried.

Rater remembers Wechsler as a quick study. “These television shows may look easy, but it is tricky,’’ she says. “It is like a jigsaw puzzle, and Pam is good at it.’’ The life of a television writer is stressful, full of deadlines and uncertainty, but it suited Wechsler’s temperament. “You have to keep your cool, and she is calm and thoughtful and not hysterical,’’ Rater says.

Those are qualities she brought to the courtroom as well, according to Gerry Leone, a longtime friend and former Middlesex County district attorney. “She is fearless,’’ he says. “She is tough, and she is serious and single-minded.’’

Wechsler and Leone were friends as young lawyers, and in 2011 she moved back to Boston for personal reasons and ended up working as a prosecutor for Leone at Middlesex for a few years. But she still had the writing bug — and continued to moonlight as a consultant. She landed a gig on “The Judge,’’ a crime film starring Robert Duvall, Robert Downey Jr., and Billy Bob Thornton.

It was Thornton who convinced her to switch careers — yet again. He was playing the prosecutor in the film, shot in Massachusetts, and the two became friendly on the set at a warehouse in Norwood. “She is smart and funny and has a dark sense of humor like I do,’’ Thornton says. “I would ask her stuff I needed to know for my character, but I also asked her things like who was the creepiest guy she ever prosecuted.’’

When she told him about a story she was developing for a television series, the much-lauded actor and Academy Award-winning screenwriter stopped her in her tracks. “I said, ‘Forget that. Write a book. Write your story and then later on you can make it into a movie.’?’’

She quit her legal job and gave herself a year to write the novel. “You just have to go for it sometimes,’’ she says. She enrolled in a novel-writing workshop at GrubStreet, the Boston creative-writing center, in January 2014, had a first draft by April, and a three-book deal by October.

The former prosecutor believes in the motto “Write what you know.’’ In the Boston-based “Mission Hill,’’ one of the characters, a thug named Orlando Jones, bears similarities to local gang member Ricardo Gittens, whom Wechsler investigated in 1995 for a drive-by shooting that killed one person and left two seriously injured. Gittens was also suspected to be the driver of the getaway car in McLaughlin’s murder. “Mission Hill,’’ not so coincidentally, centers on the death of a prosecutor.

Wechsler may start with facts from familiar cases, but the work, she says, is pure fiction. And while she does know her way around clothing boutiques, she isn’t her protagonist Abby Endicott, a Brahmin criminal prosecutor whose taste runs to Ferragamo shoes and Birkin bags. “Just for the record, I enjoy knowing about fashion, but I am not Abby,’’ she says. “It’s not my world.’’

Wechsler also will bring her courtroom experience to “Doubt,’’ which stars Katherine Heigl as a defense lawyer. She is moving back to Los Angeles to begin work on the series.

Besides leaning on the professional, Wechsler also makes use of the personal in her writing. In the novel, prosecutor Endicott also counts killers as a soporific, and her family tries to get her to switch careers, to no avail. Wechsler’s own family worried about her, but they understood her dedication. “They knew I got tremendous satisfaction from it,’’ she says. “But I don’t think they knew that I was counting killers in my mind — at least not until they read my book.’’

Patti Hartigan can be reached at pattihartigan@gmail.com.