Duignan first played for Offaly as a member of the minor team during the 1986 Leinster Championship. He made his first appearance for the team on 24 May 1986 in a 2-08 apiece draw with Kilkenny. On 13 July 1986, Duignan lined out at full-forward when Offaly faced Wexford in the Leinster final. He was switched to midfield in the second half and ended the game with a winners' medal after the 4-07 to 1-05 victory. On 7 September 1986, Duignan was again selected at full-forward when Offaly qualified to play Cork in the All-Ireland final. He scored two points from play and claimed an All-Ireland medal following the 3-12 to 3-09 victory.