The family records that William John Thomson had one son, William Thomas Thomson, who had a son Spencer Campbell Thomson, but there the trail ends. Any leads about the early Thomson family history would be welcomed by the Thomson family.

William John Thomson was originally taken to London where he learned to paint and exhibited at the Royal Academy from 1795 to 1843. He moved to Scotland in 1812 where he painted many miniatures and was elected to the Royal Scottish Academy in 1829.

On 12 May 1797 he married Helen Colhoun in Edinburgh. According to Foskett, he was offered a knighthood, but declined.

In 1832 he painted a miniature of the well known novelist Mrs Elizabeth Gaskell (1810-1865) (nee Elizabeth Stevenson) who wrote various books, including "Cranford". Elizabeth Gaskell being the step-daughter of Thomson's sister.

Johnson observed of his work; "His subjects dace slightly to the right; their features are emphatically delineated, the left eye appearing overly large. A pink tonality suffuses the paintings, reddish-brown shading models the forms, and brown hatching often makes up the background."

Although the pink tonality is not as obvious in this example, it can be seen in her face, together with the other characteristics, in the close-up image. William John Thomson died in Edinburgh on 24 March 1845.