With a reputation thus secured and plenty of family interest in his career, Duff had little difficulty progressing, being promoted to commander in 1790 and then Post Captain in 1793, a meteoric rise resulting from the growth of the Navy in the buildup to war during this period. It was at this time that he married his childhood sweetheart, Sophia Dirom (sister of Alexander Dirom) in Edinburgh, and that his son Norwich Duff (later to become an admiral in his own right) was born. In the next ten years, Duff commanded , and all very capably, but without winning the acclaim of some of his contemporaries, particularly those in the Mediterranean under Nelson.