William Larry Stewart II aka Billy Stewart (March 24, 1937 – January 17, 1970) was an American rhythm and blues singer and pianist who was popular during the 1960s.

Born in Washington, D.C., Stewart was 12 years old when he began singing with his younger brothers Johnny, James, and Frank as The 4 Stewart Brothers, and later went on to get their own radio show every Sunday for five years at WUST-AM in Washington, D.C. He was a graduate of Armstrong High School.

Stewart made the transition to secular music by filling in occasionally for The Rainbows, a D.C. area vocal group led by the future soul star, Don Covay. It was through The Rainbows that Stewart met another aspiring singer, Marvin Gaye. Rock and roller Bo Diddley has been credited with discovering Stewart playing piano in Washington, D.C. in 1956 and inviting him to be one of his backup musicians.

By 1955, this led to a recording contract with Diddley's label, Chess Records and Diddley played guitar on Stewart's 1956 recording of "Billy's Blues". A strong seller in Los Angeles, "Billy's Blues" reached the sales top 25 in Variety magazine. Stewart then moved to Okeh Records and recorded "Billy's Heartache", backed by the Marquees, another D.C. area group which featured Marvin Gaye.

Back at Chess in the early 1960s, Stewart began working with A&R man Billy Davis. He recorded a song called "Fat Boy" and then had additional success with his recordings of "Reap What You Sow" and "Strange Feeling", both making the Billboard Hot 100 and the Top 30 in the R&B charts.

Major chart success was not far away and in 1965, Stewart recorded two self-written songs, "I Do Love You" (#6 R&B, #26 Pop), which featured his brother Johnny Stewart as one of the backing vocalists with his partner James English, and "Sitting in the Park" (#4 R&B, #24 Pop). His idiosyncratic improvisational technique of doubling-up, scatting his words and trilling his lips made his style unique in the 1960s.

In 1966, Stewart recorded the LP Unbelievable. The first single released from that album was Stewart's radical interpretation of the George Gershwin song, "Summertime", a Top 10 hit on both the pop and R&B charts.

The follow-up single was Stewart's cover version of the Doris Day hit "Secret Love", which reached the Pop Top 30 and just missed the Top 10 on the R&B chart. Stewart continued to record throughout the remainder of the 1960s on Chess without major success. A weight problem worsened, and he developed diabetes. Stewart suffered minor injuries in a motorcycle accident in 1969.