Sheriff Duff was appointed Director of the Judicial Institute for Scotland in September 2014, having been Deputy Director since 2011.

He qualified as a solicitor in 1977, and worked as a procurator fiscal depute from 1977-1981 in Lanark, Hamilton, Glasgow, Edinburgh and Crown Office. From 1981-2004 he was a solicitor in private practice undertaking exclusively criminal defence work. He qualified as a solicitor advocate in 1993 as one of the first group to do so. In 2004 he was appointed as a resident sheriff based at Dundee.

He is a former member of the Law Society Council, the McInnes Committee on Summary Justice Reform, the Parole Board and the McLeish Committee on the use of imprisonment.