He was brought into the Test team for the Fifth Test at Melbourne which replaced the Victoria second tour match against the MCC in the 1970-71 Ashes series. Brought in as a fast-medium seam bowler to replace the injured Garth McKenzie, the unfortunate Duncan could only make 3 with the bat and take 0/30 with the ball in the first innings, but did not bat or bowl in the second and took no catches. He was dropped for the Sixth Test in favour of Dennis Lillee. He also represented Australia in 1971-72 in one match against Gary Sobers' Rest of the World XI.
He played for Queensland from 1964-65 to 1970-71, then for Victoria in 1971-72 and 1972-73. His best performance was 8 for 55 and 5 for 70 against Victoria at Melbourne in December 1970.