Duncan, who was handed the role yesterday at the organisation's AGM, is MD of the Edinburgh-based lobbying and PR company Message Matters, which has been an APPC Scotland member for two years.
Duncan replaces Illiam Costain McCade as chairman of APPC Scotland.
He said: "Now, more than ever, the public needs to understand and trust the role of lobbyists and political consultants, and I'm looking forward to helping the APPC in Scotland play a wide role in encouraging that process.
"With differing approaches to lobbying legislation north and south of the border, we must be engaged with the Holyrood process as it moves to consider options for legislation and widen awareness of the APPC role in ensuring transparency, openness and enforcing the highest standards among members."
Welcoming Duncan, Iain Anderson, chairman of the APPC, thanked McCade for his work leading the Scotland branch and added that the self-regulatory body had a strong leadership team throughout the UK ahead of what was set to be "a pivotal 12 months" for the lobbying industry.