A founder of Aberdeen Methodism, he was born in the town and educated at Marischal College before an apprenticeship to medicine. In 1741 he studied anatomy and midwifery in Edinburgh and about 1743 went to Wrexham as a surgeon-apothecary. Known there as a Methodist, he successfully treated without charge the future itinerant Thomas Olivers. Returning to Aberdeen in 1752, he set up an apothecary's shop. About 1759 in London, he and a few friends heard John Wesley preach and on their return home they established a Methodist society, with Memis as one of the class leaders. Christopher Hopper visited a few months later, followed by Wesley and Olivers, whom Memis entertained at his house. In the absence of an itinerant, Memis threw his weight about and caused irritation in the Aberdeen society, but another visit from Hopper put things right.
In 1764 he published The Midwife's Pocket Companion and gained his MD from St. Andrews. In 1766 he became one of the managers of Aberdeen Infirmary, whose royal charter described him as MD, but other MD holders as 'Physician', a higher designation. When they refused to alter this, he took them first to the local court, and then on appeal to the Court of Session. Memis lost and had to pay heavy damages, though he was never removed from the Infirmary management. He was undoubtedly a difficult man, and not helped by his deafness. In 1785 he published A Treatise on the Prevention and Cure of Diseases in General, based on his conviction that God's intention is for people to be healthy. The fact that the itinerant stationed in Aberdeen was lodging with him indicates that he probably remained a Methodist.