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Maskeylyne was educated at Westminster school with a good grounding in classics, and tutored in his vacations in writing and arithmetic. His interest in optics and astronomy led to his study of mathematics as the essential tool for their proper study. He applied his knowledge to other aspects of natural philosophy, especially mechanics, pneumatics, and hydrostatics, first at Catherine Hall and then Trinity College Cambridge, graduating in 1754 as Seventh Wrangler. He was ordained in 1755 and accepted a curacy at Barnet in Hertfordshire, devoting his leisure hours to assisting the Astronomer Royal, James Bradley, in computing tables of refraction. Bradley's influence with the Royal Society sent Maskelyne in 1761 to the island of St Helena to observe the Transit of Venus. This was unsuccessful because of cloud cover. However, he kept tidal records and determined the altered rate of one of Shelton's clocks. His observations regarding the method of determining longitude at sea made on the voyage were more successful. He used the lunar tables of Tobias Mayer which had been submitted in 1755 to support his application for a parliamentary bounty offered for discovery of longitude at sea. The instrument used was a reflecting quadrant of the type invented by John Hadley in 1731. Maskelyne's second voyage, to Bridgetown in Barbados in 1764, was to assess the accuracy of the rival chronometer method of longitude determination championed by John Harrison, and two other methods based on observations of the satellites of Jupiter and on occultations of stars by the moon. He attended the Board of Longitude meeting of 9 February 1765 where the sums to be awarded to Harrison and Mayer were specified, where he testified to the usefulness of the lunar-distance method for finding longitude at sea to within one degree or 60 miles, and proposed the practical application of this method by a nautical ephemeris with auxiliary tables and explanations. This last resulted in the publication of the Nautical Almanac for 1767, which Maskelyne continued to supervise until his death and was his major contribution to astronomical science. He was responsible for the publication of Mayer's lunar theory (1767), his solar and lunar tables (1770) and the preparation of 'Requisite Tables' (1767) for eliminating the effects of astronomical refraction and parallax from the observed lunar distances. As Astronomer Royal he also assessed the large numbers of chronometers submitted for official trial by such pioneers of watchmaking as John Arnold, Thomas Mudge and Thomas Earnshaw. This led to the establishment of a consistent system of rating and the introduction in 1823 of trial or test numbers, modified by George Airy in 1840 to a system which is still used. In 1774 with the aid of Charles Hutton and John Playfair he determined the earth's density in a famous experiment on Mt Schiehallion in Scotland, the first convincing experiment demonstrating the universality of gravitation, meaning it not only operates between the bodies of the solar system but also between the elements of matter of which each body is composed. For this he was awarded the Copley Medal of the Royal Society in 1775. He was elected in 1802 one of eight foreign members of the French Institute. He died while working at the Observatory in 1811.