William B. Magnarelli (born March 20, 1949) is an American politician and member of the New York State Assembly. He has represented the 129th district since 1999 as a Democrat.
Magnarelli's district includes the Northside, Westside, Eastwood and Valley areas of the City of Syracuse, as well as the towns of Geddes and Van Buren. In 1998, he won the election for an open seat.
Magnarelli grew up in Syracuse, attended Our Lady of Pompei School and St. John the Baptist Academy. He received his bachelor's degree from Syracuse University in 1970, majoring in history. He attended Syracuse University Law School, graduating with honors in 1973. After graduating, Bill Magnarelli served in the U.S. Army Reserve for six years, attaining the rank of captain.