Marion Miley was born in Philadelphia in 1914 to Fred Miley and Elsa Ego Miley. As a child she moved to Fort Pierce, Florida, in the 1920s, following her father's employment as a golf pro. It was in Fort Pierce that Miley first played golf, when she was twelve years old. She attended and graduated from St. Lucie County High School before the family moved to Lexington, Kentucky, in 1930. Miley initially wanted to be a musician or work in the field of medicine, and entered Florida State College For Women where she studied music and physical education. However, she dropped out in 1932 to focus on golfing. Miley returned to Lexington, finding work inspecting gas stations and advertising for Standard Oil.
Miley saw her first major golfing success in 1931, when she won the Kentucky state championship, a title she successfully defended the following year. She first participated in the United States Women's Amateur Golf Championship in 1933. One year later, Miley participated in the Orange Blossom Tour in Florida for the first time. She saw great success as a golfer, winning many major tournaments in the United States. Miley played for the United States in the Curtis Cup in 1934, 1936, and 1938. The following year she was ranked first in the United States. In 1938 Miley made it to the semifinals of the Women's Amateur, but was defeated by Patty Berg. In 1939 she was ranked second in the United States. She played in 41 major golfing tournaments from 1931 to 1940, winning 22.
A reporter described Miley as the "most photographed golfer in the world.
On September 28, 1941, Miley was murdered at the Lexington Country Club, which her mother had managed. Her body was discovered around five in the morning, after Miley's mother, who herself had been shot three times, crawled 200 yards (180 m) to get attention and help. The killers had been robbing the club.
Marion Miley's funeral took place on October 1, 1941, and was attended by over 1,000 people including the golfers Berg and Helen Dettweiler. Her death was widely covered in contemporary news publications around the world, and the three men involved in her killing were found quickly, placed on trial on December 8, 1941, and executed on February 26, 1943. The Lexington Country Club created the Marion Miley Memorial Golf Tournament in her memory.