[1] Under the patronage of Arthur Jones Nevill, Ennis travelled to Italy to study, arriving in Rome in late January 1954.
He studied at Accademia del Nudo in 1755 under Anton Raphael Mengs and Pompeo Batoni, and later visited Florence.
At Accademia di San Luca he won 7th prize for painting at the triennial competition in November 1754.
At the home of Arthur Jones Nevill at 14 Rutland Square, Dublin, Ennis painted a set of 4 lunettes on a ceiling, 3 are now held in the collection of the National Gallery of Ireland.
He was appointed to succeed Robert West as master of the school of figure drawing, Shaw's Court, Dublin on 10 May 1763.