Nicol was born in Edinburgh on 12th January 1856, the second son of the Scottish genre painter Erskine Nichol RSA, ARA (1825–1904) and his first wife Janet (née Watson and also known as ‘Jessie’). They had married in June 1851. John’s older sister, Jane Margaret, was eight at the 1861 census; an elder brother, James Watson, was seven. In 1863 their mother died and they moved to London where, in 1865, their father remarried to Margaret Mary Wood (1831/1832–1919) by whom he had a daughter and two further sons, all born in Kensington and baptised at St Luke’s, Chelsea. The first, Elizabeth, was born on 9th February 1866 and the boys were Erskine Edward Nicol (b.12 May 1868) and Percy Wood Nicol (b.20 May 1871). In 1879 Erskine senior and his second family returned to Edinburgh and at the 1891 census Erskine Edward was noted as an art student and Percy as a medical student there. The former became a widely travelled painter of landscape and genre scenes who exhibited six works at the Royal Academy from 1890 to 1900, lived partly in Cairo from about 1893 and finally at Cabrerets (Lot) in France, where he died on 13th May 1926, just before John Watson. By 1901 Percy had begun a long career as a general medical practitioner in London: he died at Reigate in 1943. Their sister Elizabeth last appears at home, aged 15, in the 1881 census, with no obvious later marriage or death record.