He was the father of Mervyn A. Ellison, the senior professor of the School of Cosmic Physics at Dunsink Observatory from 1958 to 1963.
In 1899 he returned to Ireland to become secretary of the Sunday School Society, a post which he held for three years before accepting the incumbency of Monart, Enniscorthy, moving in 1908 to become Rector of Fethard-on-Sea with Tintern in Wexford.
Ellison had developed an interest in astronomy, having been introduced to practical optics by Dr N. Alcock of Dublin and set up his first observatory at Wexford.
[4] His book The Amateur's Telescope (1920) is still considered a standard for telescope-makers and a forerunner of the more extensive series on the same topic by Albert Graham Ingalls.
Working with his son Mervyn, he made many measurements of binary stars using the observatory's 10-inch Grubb refractor telescope and even discovered a new one close to Beta Lyrae, and according to Patrick Moore, was one of the few people to have observed an eclipse of Saturn's moon Iapetus by Saturn's outermost (A) ring on 28 February 1919.