He was born in Woodsfield, Ohio and began attending Ohio State University in Columbus in 1927. He began teaching English at OSU as a university fellow in 1932 during the final year of his PhD and was given his first post as a university professor in 1934 at Carroll College in Helena, Montana. In 1936 he was dismissed from a position at the State College of Washington due to the portrayal of prostitution in his novel Angels on the Bough. He moved to Chicago, teaching at Loyola until 1946 and then at DePaul University. In 1952 he began tattooing in Chicago under the name Phil Sparrow partly because he did not want to jeopardize his teaching job at DePaul. He stopped teaching two years later to write and tattoo full time.

In 1932 he was taking college courses from Clarence Andrews, who had written a book which was the vehicle for Maurice Chevalier's first American movie Innocents of Paris (1929). Mr. Andrews spent half the year in Paris, where he visited Gertrude Stein many times and then returned to teaching for six months in the U.S, where he told Steward about her. After Andrews died suddenly in 1932, Steward wrote to tell her of his death, and began a long correspondence and friendship with Stein. He visited Paris in 1937 and met her and Alice B. Toklas with whom he corresponded for 20 years after Stein's death. He also met with many other literary figures such as Lord Alfred Douglas (the lover of Oscar Wilde), Thomas Mann, and André Gide. Gide once loaned to him for an evening the beautiful young Arab boy that Gide had brought from North Africa to France. Steward's 1981 memoir Chapters from an Autobiography detailed these relationships, as well as other experiences. He also edited the book Dear Sammy: Letters from Gertrude Stein and Alice B. Toklas (Houghton Mifflin, 1977), and wrote two "Gertrude Stein-Alice B. Toklas Mysteries" featuring the famous couple as detectives. Steward was also introduced to Thornton Wilder by Gertrude Stein, who at the time regularly corresponded with the both of them. Wilder famously drafted the third act of Our Town during a brief affair with Steward in Zurich on their first meeting.

Steward met famed sex researcher Alfred Kinsey around 1949 and became an unofficial collaborator, helping Kinsey find new contacts. In 1949, he participated in a BDSM scene for Kinsey to film, with a sadist that Kinsey flew in from New York. He said Kinsey was "as approachable as a park bench" and described him as a liberating influence.

In the early 1950s he made pornographic drawings, many of them based on his own Polaroid photographs. Some of his art was published in the trilingual Swiss homosexual journal Der Kreis (The Circle).

In the 1960s Steward began writing gay erotica under the name Phil Andros. His works dealt with rough trade and sadomasochistic sex. Since the legality of gay erotica was still questionable, its authors and publishers had little recourse against piracy; Steward's own San Francisco Hustler was published without permission by Cameo Library as Gay in San Francisco by "Biff Thomas". The name Phil Andros, which he used both as a pen name and the name of his protagonist, comes from the Greek words for love and man.

As a tattooist and man of letters he drew the attention of Cliff Ingram, aka Cliff Raven, and from his Oakland studio, Don Ed Hardy. He mentored both into the profession. Cliff Raven became famous as a tattooist in Chicago, and by mentoring others, generated a line of noted tattooists (Dale Grande, Robert Benedetti, Bob Roberts, Pat Fish, and Thomas Raven among others).

Steward died at age 84 of chronic pulmonary disease in Berkeley, California.

As Phil Andros:

• The Motorcyclist (1953)
• $tud (1966)
• The Joy Spot (1969)
• My Brother, the Hustler (1970; later published as My Brother, My Self)
• San Francisco Hustler (1970; later published as The Boys in Blue)
• When in Rome (1971; later published as Roman Conquests)
• Renegade Hustler (1972; later published as Shuttlecock)
• Below the Belt and Other Stories (1975)
• The Greek Way (1975; later published as Greek Ways)
• Different Strokes: Stories (1984)

As Samuel M. Steward:

• Pan and the fire-bird (1930; short stories)
• Angels on the Bough (1936)
• Dear Sammy: Letters from Gertrude Stein and Alice B. Toklas (1977, ed.)
• Parisian Lives (1984; novel)
• Chapters from an autobiography (1981; memoir)
• Murder Is Murder Is Murder (1985; Gertrude Stein-Alice B. Toklas Mystery)
• The Caravaggio Shawl (1989; Gertrude Stein-Alice B. Toklas Mystery)
• Bad Boys and Tough Tattoos: a Social History of the Tattoo with Gangs, Sailors, and Street-Corner Punks, 1950-1965 (1990)
• Understanding the Male Hustler (1991)
• Pair of Roses (1993)