He published important works on botany, zoology, and natural theology. His classification of plants in his Historia Plantarum, was an important step towards modern taxonomy. Ray rejected the system of dichotomous division by which species were classified according to a pre-conceived, either/or type system, and instead classified plants according to similarities and differences that emerged from observation. He was the first to give a biological definition of the term species.
John Ray was born in the village of Black Notley in Essex. He is said to have been born in the smithy, his father having been the village blacksmith. He was sent at the age of sixteen to Cambridge University: studying at Trinity College. His tutor at Trinity was James Duport, and his intimate friend and fellow-pupil the celebrated Isaac Barrow. Ray was chosen minor fellow of Trinity in 1649, and later major fellow. He held many college offices, becoming successively lecturer in Greek (1651), mathematics (1653), and humanity (1655), praelector (1657), frias (1657), and college steward (1659 and 1660); and according to the habit of the time, he was accustomed to preach in his college chapel and also at Great St Mary's, long before he took holy orders on 23 December 1660. Among these sermons were his discourses on The wisdom of God manifested in the works of the creation, and Deluge and Dissolution of the World. Ray was also highly regarded as a tutor and he communicated his own passion for natural history to several pupils. It has been generally asserted that Willughby was Ray's pupil at Cambridge, but what little evidence exists on the matter is rather against this supposition.
After leaving Cambridge in 1662 he spent some time travelling both in Britain and the continent. In 1673, Ray married Margaret Oakley of Launton; in 1676 he went to Middleton Hall near Tamworth, and in 1677 to Falborne (or Faulkbourne) Hall in Essex. Finally, in 1679, he removed to his birthplace at Black Notley, where he afterwards remained. His life there was quiet and uneventful, although he had poor health, including chronic sores. Ray kept writing books and corresponded widely on scientific matters. He lived, in spite of his infirmities, to the age of seventy-seven, dying at Black Notley. He is buried in the churchyard of St Peter and St Paul where there is a memorial to him.
At Cambridge, Ray spent much of his time in the study of natural history, a subject which would occupy him for most of his life. When Ray found himself unable to subscribe as required by the ‘Bartholomew Act’ of 1662 he, along with 13 other college fellows, resigned his fellowship on 24 August 1662 rather than swear to the declaration that the Solemn League and Covenant was not binding on those who had taken it. Tobias Smollett quoted the reasoning given in the biography of Ray by William Derham:
"The reason of his refusal was not (says his biographer) as some have imagined, his having taken the solemn league and covenant; for that he never did, and often declared that he ever thought it an unlawful oath: but he said he could not say, for those that had taken the oath, that no obligation lay upon them, but feared there might."