Lawrence was a highly skilled draftsman. He soon abandoned pastels but continued to make portraits in pencil and chalks. These were separate commissions and were rarely studies for paintings, as it was his usual practice to make a careful drawing of the head and sometimes the whole composition on the canvas itself and to paint over it. There are highly interesting references to his working methods in Joseph Farington's Diary.

After the death of Reynolds, Lawrence was the leading English portrait painter. His works exhibit a fluid touch, rich colour, and great ability to realize textures. He presented his sitters in a dramatic, sometimes theatrical, manner that produced Romantic portraiture of a high order. After the death of John Hoppner (Hoppner, John) in 1810 he was patronized by the Prince Regent, who knighted him in 1815 and sent him in 1818 to the political congresses of Aix-la-Chapelle and Vienna, where he painted 24 large full-length portraits of the military leaders and heads of state of the Holy Alliance. Executed with verve and elegance, these works now hang together in the Waterloo Chamber at Windsor Castle—a unique historical document of the period. By these works Lawrence was recognized as the foremost portrait painter of Europe. On his return to England in 1820 he was elected president of the Royal Academy.

Lawrence was also a distinguished connoisseur. His collection of old-master drawings was one of the finest ever assembled, and he was instrumental in securing the collection of Greek sculptures known as the Elgin Marbles for the nation and in the founding of the National Gallery.