His picturesque style was likened to that of William Mulready and he was praised by such artists as J. M. W. Turner, David Roberts and Thomas Creswick.

It is believed that Blacklock may have seen the cleaning of old masters in the National Gallery in 1844–45, which would have been an invaluable experience in terms of the evolution of his own technique.

[2] In November 1855 his youngest brother Thomas had him admitted to the Crichton Royal in Dumfries, suffering from an illness described as "monomania of ambition and general paralysis.

Geoffrey Grigson had written in the mid-twentieth century that "Blacklock, I reflect, belongs to the generation of Courbet, that creative wonder between Romanticism and Impressionism: he comes after Constable and after Corot,"[12] adding that Blacklock participated differently in a naturalism of vision and imagination which changed the arts by the middle of the 19th century, and was related to a broader artistic response at the time to newly valued works of the Italian Renaissance by Giorgione and Giovanni Bellini.

Writing in a Sotheby's sale catalogue in 2010, Christopher Newall noted that, "Although hard to place in the evolving pattern of progressive landscape painting in the mid-nineteenth century, Blacklock is an important and intriguing figure who may be regarded as a pivot between the early nineteenth-century landscape school and the achievements of Romanticism, and the earnest and obsessive innovation of the Pre-Raphaelite school.