In 1736 Grant wrote a pamphlet "Remarks on the State of the Church of Scotland with respect to Patronages, and with reference to a Bill now depending before Parliament", On 20 June 1737 he succeeded Charles Erskine of Tinwald as Solicitor General, and on 28 August in the following year was constituted one of the commissioners for improving the fisheries and manufactures of Scotland. Upon the retirement of Robert Craigie, Grant was appointed Lord Advocate on 26 February 1746, and on 20 May following the assembly held that the lord advocate could not act as procurator and clerk, and that consequently these offices were vacated.