Bill Mayhew attended Mooresville High School, where he excelled in football, baseball, and wrestling. As a wrestler, he became a two-time WNCHSAA state champion. After graduating from high school in 1959, Mayhew played football and wrestled at Appalachian State University, where he was a three-year starter and letterman in both sports. He earned a degree in Health and Physical Education from Appalachian in 1963 and later went on to obtain master's degrees in Health and Physical Education and Administration.

In 1963, Mayhew began his coaching career as the head football and wrestling coach at Troutman High School. In 1966, Troutman was replaced by the newly built South Iredell High School, and Mayhew continued as the head wrestling and football coach there. He coached football for 33 seasons until his retirement from education in 1996. During his tenure as head football coach, Mayhew achieved 13 consecutive winning seasons and amassed 196 career wins. He is still the head wrestling coach at South Iredell, completing his 60th season with the Vikings in 2024.

With 922 career dual wins, Mayhew broke the North Carolina state record in wrestling in 2024, a record he previously held. His teams won four WNCHSAA tournament championships (1970, 1972, 1974, 1976) and the NCHSAA state tournament championship in 1986, which was the last year when all classifications were combined. He enjoyed 38 consecutive winning seasons, and from January 1972 to January 1975, his teams achieved a 52-match winning streak.

In 1997, Mayhew was inducted into the charter class of the North Carolina Chapter of the National Wrestling Hall of Fame. He is also a member of the NCHSAA Hall of Fame (1998), the Mooresville High School Hall of Fame (2006), The South Iredell Hall of Fame (2011), and the Iredell County Sports Hall of Fame (2016). In 2013, Mayhew was named one of the "100 Coaches to Remember" by the NCHSAA in celebration of their 100th anniversary. In 2022, the North Carolina Wrestling Coaches Association established a "Legacy in Wrestling Award" as a tribute to Coach Mayhew, making him its inaugural recipient.