Ms. Garwood built a wide fan base — writing more than 30 books and selling more than 35 million copies — with tales that mixed the hot passions of the romance genre and the detail-rich storytelling of a historian or whodunit writer. Her heroines tended to be wily and resilient but also could be quirky and witty, a reflection of the collection of women in her own Irish American upbringing.

The sex scenes were steamy but intentionally dialed down. “I want them to be romantic but not too graphic,” Ms. Garwood wrote in a reader question-and-answer forum hosted by the book review site Goodreads. “I don’t want them to be the ‘same old, same old,’ and that is tricky.”

In some books, she used recurring characters such as the Clayborne clan in her “Rose” series that began in 1995 with “For the Roses.” The story, which mostly unfolds in the Montana territory in the late 19th century, was adapted into a popular 1997 TV movie that premiered on CBS, “Rose Hill,” starring Jennifer Garner.

Critics at times picked apart Ms. Garwood’s plots as formulaic and her narrative style as clunky, but her admirers were more than forgiving. Ms. Garwood was a headliner at romance-fiction conventions and book events. Ms. Garwood’s personal backstory, which she retold often, also became part of her attraction.

She missed long stretches of school as a girl because of illnesses, including a lengthy recovery after her tonsils were removed when she was 6. Even at 11, she still struggled to read. At a church-run summer remedial reading class, a math teacher, Sister Mary Elizabeth, was passing in the hall. She was asked to be Ms. Garwood’s tutor.

“She taught me to love the written word,” said Ms. Garwood. She was introduced to Nancy Drew mysteries and the short stories of O. Henry. Ms. Garwood needed to keep a dictionary nearby to look up words. The summer was so pivotal for Ms. Garwood that she named her daughter Elizabeth.

Her Catholic schooling also helped shape her future work. Nuns, churches and religious symbolism run through many of Ms. Garwood’s novels. In “The Prize” (1991), a Saxon woman in 11th century England flees her castle disguised as a nun to escape the juggernaut of the Norman invasion. She is later captured and finds love with the baron who led the onslaught.

The idea for “Heartbreaker,” a novel published in 2000 and set in the late 1990s, came to Ms. Garwood as she looked over a confessional in a Catholic church in London. “What if you tell a sin you haven’t committed yet,” Ms. Garwood recalls thinking.

In the novel, a killer tells a priest of his plans to find another victim, saying he wanted the woman to know in advance to make the stalking more of a challenge. The twist is that the intended victim is the priest’s sister. A dashing FBI agent leads the hunt; romance ensues.

The book marked a new direction for Ms. Garwood into contemporary thrillers with, of course, ample room for romance and sex. In “Mercy” (2001), readers are introduced to federal prosecutor Theo Buchanan, who becomes involved in a probe of a killing and crooked investments in New Orleans and bayou country.

The Buchanan family keeps popping up in other books: FBI agent Alec Buchanan in “Murder List” (2004) is assigned to protect a woman from a killer; Boston Police Det. Dylan Buchanan protects another woman in “Slow Burn” (2005); and a sister, Jordan Buchanan, is at the center of a Texas murder mystery in “Shadow Dance” (2006).

In her last book, “Grace Under Fire” (2022), a character named Michael Buchanan — a former Navy SEAL and high-powered Boston lawyer — becomes the bodyguard for a young heiress caught up in a web of violence.

Ms. Garwood bristled at being labeled a purveyor in outmoded literary stereotypes of strong men and women in distress. The women in her novels, she insisted, always end up the intellectual and sexual equal of any man — and often are shown to be more clever and intuitive.

“I learned early on that if I wanted to be heard,” she said, “I had to have a strong voice. I also got my warped sense of humor from my family.”

Encouraged by a professor

Julia Elizabeth Murphy was born Dec. 26, 1944, in Kansas City, Mo., one of six girls and a brother. Her father, who served in the same World War I unit as future president Harry S. Truman, did various jobs and was an amateur boxer; and her mother was a homemaker.

After raising a family, Ms. Garwood began studying nursing at Avila College in Kansas City. She added history as a double major after taking a course in Russian studies. (Ms. Garwood grew up believing her name was Julie but later found documents that showed her real name was Julia.)

A professor, impressed by her essays, encouraged her to take time off to write. The result was the manuscript of young adult fiction, “A Girl Named Summer” (eventually published in 1986), and the framework for a historical novel about a noble woman in feudal Britain who seeks revenge for the slaying of her family.

At a writer’s conference at Avila in the early 1980s, Ms. Garwood struck up a conversation with an agent, Andrea Cirillo. “[She] who took pity on me standing by the corner like a wallflower,” Ms. Garwood said.

Cirillo asked about Ms. Garwood’s interests as a writer. Cirillo wasn’t interested in authors of children’s books. “Then she asked me what else I had,” Ms. Garwood recalled. She described the historical romance she had written, which Ms. Garwood titled “The Warrior.” Cirillo wanted a look.

The novel, changed to “Gentle Warrior,” was published in 1985. Sales were good. Ms. Garwood was asked for another, which became “Rebellious Desire” (1986), a story about a test of wills between an English duke and a Boston woman who fled America.

Nearly every year after that, another story of long-ago romance and adventure hit the shelves. “The Bride” (1989) has a swashbuckling heroine in medieval Scotland. In the 1990 novel “Guardian Angel,” a marquis searches the slums of 19th century London in search of his brother’s killer and falls in love with a mysterious woman.

“My stories come from everywhere,” said Ms. Garwood, who also wrote several young adult-themed novels under the name Emily Chase. “I’ve always been a bit of a daydreamer, so there’s usually a story going on in my head at any given time.”

Ms. Garwood’s marriage to Gerald Garwood ended in divorce. Survivors include two sons, Gerald and Bryan, and a daughter, Elizabeth.

As her reputation grew as a writer, Ms. Garwood liked to joke about the helpful early career advice from her mother. “My mom used to say you could be anything you want to be,” Ms. Garwood recalled, “but learn to type.”