She was born Kathleen Erin Hogg in Alexandria, Louisiana, the youngest of eight children of Charles Wingrove Hogg, a disabled World War I veteran, and his wife, Gladys (Coker). As a child, she relished creating her own stories, and by age six was telling herself stories at night to help fall asleep. Her father died suddenly when Woodiwiss was only twelve, leaving her to be raised by her mother and older sisters. Woodiwiss would later remark that, "every single one of us had minds of our own even then; I was no exception. I suppose that carried over into my creations of heroines who weren't weak-willed."
At the age of sixteen, she met U.S. Air Force Second Lieutenant Ross Eugene Woodiwis at a dance. They married the following year, on July 20, 1956. She attended school locally and graduated in 1957. Her husband's military career led them to live in Japan, where she worked part-time as a fashion model for an American-owned modeling agency. After three and a half years in Japan, the family moved to Topeka, Kansas and then settled in Minnesota.. During these years, she attempted to begin a novel several times, but each time stopped in frustration at the slow pace of writing a novel longhand. After buying her husband an electric typewriter for a Christmas present, she appropriated the machine to begin her novel in earnest.
Her debut novel, The Flame and the Flower, was rejected by agents and hardcover publishers as being too long at 600 pages. Rather than follow the advice of the rejection letters and rewrite the novel, Woodiwiss instead submitted it to paperback publishers. The first publisher on her list, Avon, quickly purchased the novel. Legendary editor Nancy Coffey provided a $1500 advance and arranged for an initial 500,000 print run. The Flame and the Flower was revolutionary, featuring an epic historical romance with a strong heroine and actual sex scenes. This novel, published in 1972, sold over 2.3 million copies in its first four years of publication and is credited with spawning the modern romance genre, becoming the first romance novel "to [follow] the principals into the bedroom." The success of this novel prompted a new style of writing romance, concentrating primarily on historical fiction tracking the monogamous relationship between helpless heroines and the hero who rescued her, even if he had been the one to place her in danger. The romance novels which followed in her example featured longer plots, more controversial situations and characters, and more intimate and steamy sex scenes.
Woodiwiss had a direct impact on the career of fellow novelist LaVyrle Spencer. Soon after finding her own success, Woodiwiss read a manuscript written by Spencer, who had yet to earn a publishing contract. Woodiwiss promptly mailed Spencer's novel to her own editor at Avon. The editor purchased the novel, The Fulfillment, beginning Spencer's career. In addition, many modern romance novelists cite Woodiwiss as their inspiration. Julia Quinn remarked that "Woodiwiss made women want to read. She gave them an alternative to Westerns and hard-boiled police procedurals. When I was growing up, I saw my mother and grandmother reading and enjoying romances, and when I was old enough to read them myself, I felt as if I had been admitted into a special sisterhood of reading women."
Woodiwiss published twelve best-selling romance novels, with over thirty-six million copies in print. Woodiwiss was known for the quality of her novels rather than the quantity of works she published. She often took four to five years to write a single novel. In some cases, Woodiwiss attributed the lag in publication time to personal and health issues, while in others she confessed to having suffered burnout and needing a rest to recover her interest in writing.
All of her novels were historical romances set in varied backgrounds, including the American Civil War, 18th-century England, or Saxony in the time of William the Conqueror. The heroines of the novels are strong-willed young women with "a spark of life and determination." Woodiwiss describes her novels as "fairy tales. They are an escape for the reader, like an Errol Flynn movie."
Woodiwiss was an avid horse rider who at one time lived in a large home on in Minnesota. After her husband's death in 1996, she moved back to Louisiana. She died in a hospital in Princeton, Minnesota, aged 68, from cancer.
She is survived by two sons, Sean and Heath, their wives, and numerous grandchildren. A third son, Dorren, preceded her in death. Her final book, Everlasting, was released on October 30, 2007.