Billy MacKenzie (born 7 April 1984 in Edinburgh) is a Scottish former professional motocross racer. He competed in the Motocross World Championships from 1999 to 2013. MacKenzie is a two-time British Motocross Champion.
MacKenzie rode for the Honda factory racing team competing in the F.I.M. MX1-GP World Championships. He has also represented the United Kingdom in the Motocross des Nations. MacKenzie recorded his first and only World Championship victory when he won the MX-1 Class at the 2007 Japanese Motocross Grand Prix. In 2010, MacKenzie rode for Kawasaki in Australia.