Winslow was born in New York, on Halloween night, 1953, but grew up in Perryville, a beach town near the village of Matunuck, Rhode Island. He credits his parents for preparing him to become a writer: his mother was a librarian, and his father was a non-commissioned officer in the United States Navy who told stories and invited Navy friends who told more. From them, Winslow was inspired to become a storyteller himself. He majored in African History at the University of Nebraska.

In the late 1970s, Winslow moved back to New York City, where he first worked managing a chain of movie theaters, then as a private investigator in movie theaters and the back alleys of Times Square. His career grew even more varied; he went back to school to earn a master's degree in Military History, and led safaris in Kenya and hiking trips in China's Sichuan province. His first published novel, A Cool Breeze on the Underground (1991) was written during this time. It was the first of a series of books about investigator Neil Carey, and was not very successful. Winslow's career as an investigator would repeatedly bring him to California, to look into arson cases; his storytelling skills helped in explaining cases to juries. In the mid 1990s, he moved to California with his wife Jean and their infant son Thomas, and kept writing when he could. His thriller The Death and Life of Bobby Z (1997), was a success, and allowed him to become a full time writer. They live in Julian, California.

Winslow says he writes every day from 5:30 to 10 in the morning, then hikes six or seven miles before returning to work. He generally works on two books at a time, moving to the other when work on the first stalls. He says the longest he has gone without writing after a book is completed is five days; he calls it an addiction.

The time it takes him to write a book varies. The Death and Life of Bobby Z was written on the train between Dana Point, California and Los Angeles, one chapter per trip. The Power of the Dog took six years to research and write, including traveling to Mexico to interview people with similar experiences as its characters.