Duncan practice primarily focuses on estate planning, trusts, business matters, and federal taxation. He graduated from SMU in 1977 with a business administration degree in accounting and finance and earned his law degree from SMU in 1980. During the three years Inside Collin County Business conducted its annual awards, Duncan was voted “Best Business Lawyer” in Collin County all three years (1997-1999) and “Best Business Tax Consultant” one year (1997). Duncan was also voted "Best Attorney in Plano/Frisco" by Living Magazine for 2016, 2017, and 2018. Duncan was elected and has been serving since January 1, 2011 as Collin County's Commissioner for Precinct 4.