About this time he became a student at the Government School of Design at Somerset House, where J. R. Herbert, Richard Redgrave, and John Callcott Horsley were among his instructors.

Among patrons were John Phillip and James Nasmyth, and he was awarded a silver medal by the Society for the Encouragement of the Fine Arts.

[1] Towards the end of 1861 MacCallum painted at Fontainebleau; in 1864 he worked in Switzerland and on the River Rhine; in 1866 he was in Italy; in the winter of 1866–7 he was in the neighbourhood of Paris.

[3] He was "the Painter" who accompanied Amelia Edwards in 1873- 1874 on her Dahabiya in her best selling book "A Thousand Miles Up the Nile".

[1] The Tate Gallery acquired MacCallum's Silvery Moments, Burnham Beeches (1885), and The Monarch of the Glen; the Victoria and Albert Museum his In Sherwood Forest—Winter Evening after Rain (1881), S. Maria delle Grazie, Milan (1854), Rome from the Porta San Pancrazio (1855–6), The Burning of Rome by Nero, and the Massacre of the Christians (1878–9), and Head of Christ after Daniele Crespi.

The City of Nottingham Art Gallery bought The Major Oak, Sherwood Forest (1882), measuring about 9 ft. by 12 ft., and The Opening Scene in Bailey's "Festus".

[4] His second marriage, on 18 June 1879, was to Laura Salwey (born 1856), daughter of Ludlow solicitor Humphrey Salway.

MacCallum petitioned for a divorce from Laura in April 1888, on the grounds of her alleged adultery with Ernest Malleson.