He served an apprenticeship to a writer to the signet in Edinburgh, and became confidential clerk to Lord-advocate Sir James Montgomery, who introduced him to Mr. Wilson of Howglen, with whom he became partner.
In his earlier years he devoted much of his spare time to study, rising at four in the morning to read Greek, attending a debating society, and enrolling himself in some of the university classes, including that of moral philosophy, where he had as one of his fellow-students Dugald Stewart, with whom he became intimately acquainted.
He was a supporter of the American war of independence, a prominent abolitionist, and so strong a sympathiser with the French Revolution that he attended every anniversary of the fall of the Bastille from 14 July 1789.
He acted without fee as counsel for the political reformer Joseph Gerrald and 'other friends of the people' charged with sedition in 1793, and in 1796 was one of the minority of thirty-eight who opposed the deposition of Henry Erskine, dean of the faculty.
He is described by Lord Brougham as 'one of the most upright men that ever adorned the profession, and a man of such stern and resolute firmness in public principle as is very rarely found united with the amiable character which endeared him to private society.'