Neiman was born in Saint Paul, Minnesota, the son of Lydia Sophia (née Serline) of Braham, Minnesota and Charles Julius Runquist, who were married in 1918, and living at Grasston, Minnesota (Kanabec County) in 1921. He was of Swedish descent. His father deserted his family, and when his mother married his stepfather, John L. Niman (Neiman) in 1926, LeRoy changed to the new surname as well. His mother divorced Neiman about 1935, and married for the third time in about 1940, to Ernst G. Hoelscher, of St. Paul. She died in St. Paul, Minnesota, November 14, 1985, at age 87 years. LeRoy was raised in the Macalester-Groveland, and Frogtown neighborhoods of St. Paul. The home he lived in the longest, from about 1940 to about 1955, still stands at 569 Van Buren Avenue, in St. Paul.

Neiman served in the U.S. Army during World War II. He worked as a cook until the end of the war, when his art skills were recognized and put to use painting sets for Red Cross shows. Following his return in 1946, Neiman studied briefly at the St. Paul School of Art, then at the School of The Art Institute of Chicago on the G.I. Bill. After graduating, Neiman served on the Art Institute faculty for ten years. During the time Neiman was teaching, he was exhibiting art in competitions and winning prizes. In 1954, Neiman began his association with Playboy Magazine. Neiman had met Hugh Hefner while doing freelance fashion illustration for the Carson Pirie Scott department store chain, where Hefner was a writer. Hefner and Playboy art director Art Paul commissioned an illustration for the magazine’s fifth edition. Among Neiman’s contribution over the next 50 years, he created the Femlin character for the Party Jokes page, and did a feature for 15 years titled “Man at His Leisure,” where Neiman would paint illustrations of his travels to exotic locations.

Beginning in 1960, he traveled the world observing and painting leisure life, social activities and athletic competitions including the Olympics, the Super Bowl, the World Series, the Kentucky Derby, championship boxing, PGA and The Masters golf tournament, The Ryder Cup, the World Equestrian Games, Wimbledon and other Grand Slam competitions, as well as night life, entertainment, jazz and the world of casino gambling.  In 1998 he did all the illustrations for a special “Sports” issue of The Nation magazine, for which he received the magazine’s standard fee of $150.

Neiman sponsored and supported several organizations from coast to coast that foster art activities for underprivileged children such as The LeRoy Neiman Center for Youth in San Francisco and the Arts Horizons LeRoy Neiman Art Center in Harlem. He also has established facilities at various colleges, including the LeRoy Neiman Center for Print Studies at Columbia University in New York and the LeRoy Neiman Campus Center at his Alma Mater, the School of the Art Institute of Chicago. Neiman donated $5 million to the School of the Art Institute, which funded the construction of the Neiman Center at the School.

He received five honorary doctorates and numerous awards, a recent Lifetime achievement award from the University of Southern California, an induction into the International Boxing Hall of Fame and proclamations and citations. Most recently he received The Order of Lincoln award on the 200th birthday celebration of Abraham Lincoln given by The Lincoln Academy of Illinois. He has authored twelve books of his art. A documentary on his jazz painting, “The Big Band,” had its world premiere in Los Angeles in February, 2009.

Neiman produced about six different serigraph subjects a year, generally priced from $3,000 to $6,000 each. Gross annual sales of new serigraphs alone top $10 million. Originals can sell for up to $500,000 for works such as “Stretch Stampede,” a mammoth 1975 oil painting of the Kentucky Derby. In addition to being a renowned sports artist, Neiman has created many works from his experience on safari, including “Portrait of a Black Panther,” “Portrait of the Elephant,” “Resting Lion,” and “Resting Tiger.” Some of his other subjects include sailing, cuisine, golf, boxing, horses, celebrities, famous locations, and America at play. Much of his work was done for Playboy Magazine, for which he still illustrated monthly until his death.

Neiman worked in oil, enamel, watercolor, pencil drawings, pastels, serigraphy and some lithographs and etching. Neiman is listed in Art Collector’s Almanac, Who’s Who in the East, Who’s Who in American Art, Who’s Who in America, Who’s Who in the World. His works have been displayed in museums, sold at auctions, and displayed in galleries and online distributors. He is considered by many to be the first major sports artist in the world, challenged only in his later years by a new generation of artists like Stephen Holland and Richard T. Slone. His work is in the permanent collection of the Smithsonian, the Whitney Museum, the Brooklyn Museum, the Museum of Fine Arts in Boston, the State Hermitage Museum in Russia, Wadham College at Oxford and in museums and art galleries the world over, as well as in private and corporate collections.

Neiman married Janet Byrne in 1957. They lived in New York City, their home base for over five decades, until Neiman’s death. Their residence, inside a New York City landmark, the Hotel des Artistes over the Café des Artistes on West 67th Street, originally intended for painters, is made up of double-height rooms that overlook Central Park. Norman Rockwell once lived there, as well as celebrities Rudolph Valentino, Noël Coward and former mayor John Lindsay. Neiman’s painting studio, offices, and home are on one floor, his archives on another, his penthouse at the top.

Neiman continued to paint despite having his right leg amputated, the result of a vascular problem, at a New York hospital in April 2010. Neiman’s autobiography, titled All Told: My Art and Life Among Athletes, Playboys, Bunnies, and Provocateurs was published on June 5, 2012.

Neiman died on June 20, 2012, at the age of 91, in New York City.