William "Billy" Moses was born in Los Angeles, California. He is the son of the late Actress Marian McCargo (1932–2004) and advertising executive Richard Cantrell Moses Sr., who married in 1951 and divorced in 1963. Marian remarried in 1970 to the Republican Congressman Alphonzo E. Bell Jr. (1914–2004). Congressman Bell adopted Billy and his brothers Rick and Harry. william briefly attended Wesleyan University.

Moses is probably best known for playing Cole Gioberti in the 1980s prime-time soap opera Falcon Crest, from 1981 to 1987. Following six seasons on Falcon Crest and some episodes in the middle of the seven season, he co-starred in the early Julia Roberts film Mystic Pizza in 1988. He then co-starred with Raymond Burr in Perry Mason television films from 1989 to 1995, playing Ken Malansky, an attorney who worked with the title character Mason as a private investigator (although in his first appearance as Malansky, Moses played a law student who was defended by Mason on a murder charge). Moses returned to soap opera in 1992–93 when he played the recurring role of Keith Gray on Melrose Place. He made appearances in two Adventures of Mary-Kate and Ashley short films, The Case of the Mystery Cruise and The Case of the Sea World Adventure, both in 1995. In 1997, he played David Graysmark in the short-lived series Fame L.A. He also appeared in various television movies including Alone With a Stranger (2000), and Christmas Child (2003). Since 2005, he has appeared as Jack Davis in nine of the Jane Doe movies on the Hallmark Channel.

In 1987 he married to Actress Tracy Nelson. They divorced in 1997 and share a daughter, Actress Remington Elizabeth Moses, born in 1992. In 2000 he married Sarah Moses.