Mifsud's most notable performance was in reaching the last 32 of the 1984 World Championship, where he lost 2–10 to Terry Griffiths. He was twice World Amateur champion, in 1985 and 1986, defeating Dilwyn John 11–6 in the former and Kerry Jones 11–9 in the latter, and had reached the final in 1976, where he lost 1–11 to the rising Doug Mountjoy.