In 1747, his poem "Musaeus, a Monody on the Death of Mr. Pope" was published to acclaim and quickly went through several editions.[2] Summarizing this poem, a threnody, William Lyon Phelps writes:
Musaeus was a monody on the death of Pope, and written in imitation of Milton's Lycidas. Different poets in Musaeus bewail Pope's death; Chaucer speaks in an imitation of old English, and Spenser speaks two stanzas after the metre of the Shepherd's Calendar and three stanzas in the style of the Fairy Queen. There is nothing remarkable about these imitations....[3]
Among his other works are the historical tragedies Elfrida (1752) and Caractacus (1759) (both used in translation as libretti for 18th century operas: Elfrida - Paisiello and LeMoyne, Caractacus - Sacchini (as Arvire et Évélina) and a long poem on gardening, The English Garden (three volumes, 1772–82). His garden designs included one for the Viscount Harcourt.
He entered the Church in 1754, and in 1762 became the precentor and canon of York Minster.[4]
He was the friend, executor, and biographer of Thomas Gray, who was a great influence on his own work. In 1775 The Poems of Mr. Gray. To which are prefixed Memoirs of his Life and Writings by W[illiam]. Mason. York, was published.[5]James Boswell said that in his Life of Samuel Johnson (1791) he "resolved to adopt and enlarge upon the excellent plan of Mr Mason, in his Memoirs of Gray." Mason was also a friend of Horace Walpole[6] and Joshua Reynolds.
Two of his works of scenes at the York racecourse, "A Country Racecourse with horses preparing to start" and "A Country Racecourse with horses running". were reproduced as mezzotint illustrations in 1786 by Francis Jukes in collaboration with Robert Pollard.[8][9]
Memorial inscriptions for Mason may be found in the church at Aston near Rotherham where he was rector and at Poet's Corner in Westminster Abbey. A cenotaph was also erected by Countess Harcourt in the gardens at Nuneham Courtenay.[3][10]