This was followed by a period with his brother Walker King at Corpus Christi College, Oxford, where he was introduced to Thomas Hornsby, a priest and Savilian Professor of Astronomy, by his father's first cousin, Fletcher Norton, 1st Baron Grantley, Speaker of the House of Commons and member of the Board of Longitude, who recommended him for Cook's third voyage.

[4] Thus King's geographical positions were an important contribution to the accuracy of the various surveys carried out during the voyage and his use of the early chronometers helped prove their use at sea for calculation of longitude.

After his return to England King was very much involved in the publication of the official account of Cook's third voyage, writing the third volume at Woodstock, near Oxford, where his brother Thomas was rector of St Mary Magdalene.

He captured a French frigate, La Coquette, off Turks Island before returning to England at the end of the American Revolutionary War in 1783 with his health much impaired.

After the publication of the three-volume account of the voyage, advancing tuberculosis drove him to Nice, accompanied by his friends James Trevenen, who had served with him in the Resolution and Discovery, and Captain William Young, who had served with him in the Guernsey, where he died on 16 November 1784 at the age of 34, although the memorial tablet in Woodstock parish church states erroneously that he died in his 32nd year.