Malcolm, a sagacious historian, or rather historical critic, was born in 1768, at his paternal estate in Orkney, and educated at the grammar school of Kirkwall. Removing to Edinburgh, he studied law at the university, and took a leading part in the debates of the Speculative Society, a literary club with which the early lives of Scott, Jeffrey, Brougham, Mackintosh, and many other eminent men, were long associated. In 1784 he passed advocate, but failed to work himself into practice. He only distinguished himself at the bar on one occasion, when he undertook the defence of Joseph Gerrald on his trial for sedition in 1794. He first made himself a name in letters by finishing and carrying through the press the last volume of Henry's History of Great Britain, left incomplete by the author's death. Henry had been a staunch conservative. Laing was an equally staunch liberal. Each wrote from the stand-point of his own party, and the principles and views of politics in the last volume of the history are at signal variance with those of the other parts of the work.

Dr Parr used to speak in terms of the highest praise in regard to that part of the narrative which treats of the conduct and treatment of Perkin Warbeck.

In 1800 he published his History of Scotland from the Union of the Crowns, on the Accession of James VI. to the Throne of England, to the Union of the Kingdoms in the reign of Queen Anne. Two preliminary dissertations accompanied this work, one on the Gowry Conspiracy, and another directed against the authenticity of the poems of Ossian. In 1804 a second edition of the "History" was called for; and the author seized the occasion to add a third essay, On the Participation of Mary Queen of Scots in the Murder of Darnley. Laing's only other contribution to history was his edition of the Historie and Life of King James the Sixth, published in 1804 from a copy of the original manuscript, from which Crawford of Drumossy, historiographer to Queen Anne, had compiled his Memoirs of the Affairs of Scotland. These "Memoirs" had been written in the interest of Mary Queen of Scots, and professed to be based on a MS. history of the times. Laing discovered the original manuscript, and proved, with his usual acuteness, that Crawford had so garbled and mutilated it as to have committed "one of the grossest literary forgeries that had ever been employed to pervert the genuine history of Scotland."

In 1805 Laing married Margaret Carnegie of Craigio, in Forfarshire. Two years later he entered parliament as member for Orkney, but bad health drove him back into private life after a single session. Retiring to his native place, he recovered a little, and spent the remainder of his life in agricultural pursuits. His death took place somewhat suddenly in November 1818. To Mr Laing, as a historian, belongs the undoubted merit of having cleared away much rubbish, removed many prejudices, refuted numerous and grave errors, detected not a few impostures, and generally placed both the character and events of that portion of our national history of which he treats in a clearer and more satisfactory light than he found them. Although he had many enemies, few dared to reproach him with a disregard of truth. His sagacity and acuteness led him instinctively to results, the most of which have been confirmed by more recent investigation.