Ennis, Jacob (1728–70), portrait and historical painter, was baptised 29 February 1728 at St Peter's church, Dublin, son of James and Margaret Ennis (his father's occupation and his mother's maiden name are both unknown). He trained as an artist under Robert West (qv) at the Dublin Society school of drawing at George's Lane. During a successful student career he was awarded premiums in 1747, 1748, and 1750. Subsequently he came to the notice of Arthur Jones Nevill (qv), surveyor general of Ireland, whose patronage enabled Ennis to continue his studies in Italy. He arrived in Rome before the end of January 1754. There he shared lodgings with Robert Crone (qv) and James Forrester. In 1755 he studied at the Accademia del Nudo, whose teachers included Anton Raphael Mengs (1728–79) and Pompeo Batoni (1708–87). He also spent some time in Florence.
He continued to achieve success with his work. In November 1754 he was awarded seventh prize for painting in the triennial competition of the Accademia di San Luca. For drawings entered in the Concorso Nudo he was twice awarded third prize (June 1755, January 1756). Both of these drawings are in the collection of the archive of the Accademia Nazionale di San Luca in Rome. As well as drawing from life, Ennis also made drawings after antique statuary which he studied in Rome and Florence. Six of these drawings were bought by the collector Stephen Beckingham (1730/31–1813) of Bourne Park, Kent, whose collection also included works by the sculptor Simon Vierpyl (qv). Before returning to Ireland Ennis spent some time in Gibraltar, where he painted a number of portraits.
On his return to Dublin he established himself as a painter of portraits and historical subjects. He painted a set of four lunettes for the ceiling of the house of Arthur Jones Nevill at 14 Rutland Square, Dublin. These works, three of which are now in the collection of the NGI, depict mythological scenes after works by Pietro da Cortona (1596–1669) in the Pitti palace, Florence. On 10 May 1763 Ennis was appointed to succeed Robert West as master of the school of figure drawing, then located at Shaw's Court, Dublin. Between 1765 and 1770 he exhibited annually at the Society of Artists, showing drawings and paintings of mythological and biblical subjects as well as portraits. The identities of the sitters for these works went unrecorded. In June 1768 he was awarded a Dublin Society premium for ‘the best original history piece painted in oil colours’, and in June 1770 he, along with Henry Tresham (qv), was once again among the premium winners.
The final payment to Ennis as master of the figure drawing school was made on 9 August 1770. Soon afterwards he died from injuries sustained from falling from his horse while riding in Co. Wicklow. He never married. Robert West was reelected to succeed him in October 1770, though he died the following month and was in turn succeeded by his son Francis Robert West (qv).