Penelope Niven, a biographer who brought renewed attention to three major cultural figures of the 20th century and was the co-author of actor James Earl Jones’s autobiography, died Aug. 28 at a hospital in Winston-Salem, North Carolina. She was 75.

The cause was a probable brain aneurysm, said her daughter, Jennifer Niven McJunkin, who also is a published author.

Niven had been a homemaker and high school teacher before she turned to writing and published comprehensive biographies of photographer Edward Steichen and writers Carl Sandburg and Thornton Wilder.

She found her new calling by accident after visiting Sandburg’s home in Flat Rock, North Carolina, in the 1970s. Seeing that the writer’s papers were in disarray, Niven volunteered to put them in order.

She soon became immersed in the project, which grew to include interviews with more than 150 friends and descendants of Sandburg, who was one of the country’s most renowned writers of the first half of the 20th century. Niven told Sandburg’s former agent, Lucy Kroll, that there was enough material for someone to write a biography.

“You will write the book,” Kroll reportedly told her, “and I will represent you.”

After 14 years of work, Niven completed her well-regarded book in 1991, when she was 52. It chronicled the sweeping life of Sandburg, who memorably described Chicago as the “city of the big shoulders” and won two Pulitzer Prizes for poetry and a third for a volume of his biography of Abraham Lincoln.

Sandburg was an early multimedia star, lecturing all over the country, singing folk songs on college campuses and writing columns for newspapers. He was a self-styled “poet of the people” who often appeared on radio and television before his death at 89 in 1967.

“Sandburg was the first poet whose face was recognizable to the public,” Niven told the Chicago Tribune in 1991.

Niven retraced Sandburg’s steps back to his native Galesburg, Illinois, where he grew up as the son of Swedish immigrants.

“I took that train ride from Galesburg to Chicago,” Niven told the Tribune, “trying to feel the excitement of an 18-year-old coming here from a small town for the first time. From Union Station, I walked down to Lake Michigan to marvel, as young Carl did, at an expanse of water ‘running to meet the sky,’ as he put it.”

While working on the Sandburg biography, Niven grew interested in the life of photographer Edward Steichen, whose sister was married to Sandburg. In 1997, Niven published the first major biography of Steichen, who helped define photography as an art form and introduced the paintings of Picasso and Matisse to the United States at his New York art gallery in the early 1900s.

Niven received another career boost when Kroll, the well-connected agent, introduced her to Jones, the Broadway and Hollywood star. Though known for his booming, eloquent voice, Jones, who was born in rural Mississippi, had overcome a childhood stutter.

“There were nuances of Southern life we both understood,” Niven said in 1993, “that I think it would have been difficult for people in other regions of the country to detect.”

They worked for four years on Jones’s 1993 autobiography, “Voices and Silences,” and remained lifelong friends.

In 2012, Niven published a sympathetic 800-page biography of Wilder, the author of the novel “The Bridge of San Luis Rey” and the plays “Our Town,” “The Skin of Our Teeth” and “The Matchmaker,” which was the basis for “Hello, Dolly!” (He also wrote the screenplay of Alfred Hitchcock’s 1943 small-town thriller “Shadow of a Doubt.”)

Some critics complained that Niven shed too little light on Wilder’s apparent homosexuality, but her book brought new recognition to an all-but-forgotten author who had been among the most acclaimed American writers of the 1920s and 1930s.

“ ‘Thornton Wilder: A Life’ is the best kind of literary biography,” Washington Post contributor Dennis Drabelle wrote in his review, “one likely to send the reader back (or perhaps for the first time) to the author’s works.”

Penelope Ellen Niven was born April 11, 1939, in Waxhaw, North Carolina. Her father was a postal inspector, her mother a teacher.

Her home town, Niven said, was just like Grover’s Corners, the fictional village Wilder created for “Our Town.”

“I grew up in a little town in North Carolina, population 800,” she recalled in a 2012 NPR interview. “When I read ‘Our Town’ as a teenager, I was positive the play had been written about Waxhaw, North Carolina.”

She graduated from Greensboro College in North Carolina in 1961 and later received a master’s degree in English from Wake Forest University in Winston-Salem. She accompanied her then-husband, an academic, to Philadelphia, St. Mary’s City, Maryland, and Richmond, Indiana, before settling in Winston-Salem in the 1980s.

Her marriage to Jack McJunkin ended in divorce. Survivors include her daughter, Jennifer Niven McJunkin of Los Angeles; two sisters; and a brother.

In recent years, Niven was a writer-in-residence at Salem College in Winston-Salem and a consultant to documentary filmmakers. She lectured around the world and often presented writing seminars with her daughter, who has written several novels and nonfiction books under the name Jennifer Niven.

In her 40s, when Niven was embarking on her career as a writer, she went through a divorce and, because of a temporary medical condition, needed to wear braces on her teeth. As a way of redirecting her energy, her daughter encouraged her to learn to swim.

Years later, in her 2004 memoir “Swimming Lessons,” Niven reflected on how swimming gave her newfound confidence and represented a fresh start in life.

“I have to push the water back,” she wrote, “if I want to move forward.”