Gruner was born in Gisborne, New Zealand, younger son of Elliott Grüner, a Norwegian-born bailiff, and his Irish wife Mary Ann, who died in 1922. Gruner was brought to Sydney before he was a year old and at an early age showed a desire to draw. When about 12 years old his mother took him to Julian Ashton who gave him his first lessons in art. At 14 years of age he obtained a position in a shop where he worked from 7.40 a.m. to 9.30 p.m. to help to maintain the household after his father and older brother died.
Gruner managed to do some painting on weekends, and in the year 1901, began to send work to the exhibitions of the Society of Artists at Sydney. From around 1907 his work began to attract serious attention, one admirer was Norman Lindsay. In 1911 a small shop was started in Bligh-street, Sydney, to sell works of art produced in Australia and for a time Gruner took charge of it. He then became an assistant to Julian Ashton at the Sydney Art School, and during Ashton's illness took complete charge of the classes for about three months. In 1916 he was the winner of the Wynne art prize with a small landscape "Morning Light" which was purchased by the national gallery of New South Wales. Gruner was the winner of the Wynne prize again in 1919, and in the following year the trustees commissioned him to paint a large picture for the gallery "The Valley of the Tweed". Though this was awarded the Wynne prize in 1921 and is a capable work it scarcely ranks among his best efforts. He seldom afterwards took anything larger than a 24-inch canvas.
In 1923 Gruner visited Europe and was away for around two years. The effect of travel on his work was very noticeable. There was generally a good deal of simplification, more attention to pattern, and a freer and wider sweep of his brush. Sir William Orpen had provided constructive comments on his work which altered Gruner's style. Gruner was less interested in the problems of light and occasionally his work took on a slightly cold aspect. The changes were not always welcomed by his admirers, but Gruner was right not to allow himself to fall into a groove. Gruner held a one man show in 1927, but he was not a very productive artist and therefore was in a position to sell almost everything he produced. Gruner spent much time in finding a suitable subject, and more still in carefully considering it before a brushstroke was made. Gruner became interested in the study of light again, and some excellent work of his latest period combined the qualities of his art and his passion.
Gruner suffered from chronic nephritis and died at his home at Waverley on 17 October 1939. He was cremated with Anglican rites.
Wynne Prize wins
- 1916 - Morning Light
- 1919 - Spring Frost
- 1921 - Valley of the Tweed
- 1929 - On the Murrumbidgee
- 1934 - Murrumbidgee Ranges, Canberra
- 1936 - An Australian Landscape
- 1937 - Weetangera, Canberra
- B. Pearce, 'Gruner, Elioth Lauritz Leganyer (1882 - 1939)', Australian Dictionary of Biography, Volume 9, Melbourne University Press, 1983, pp 134-135. Retrieved on 30 December 2008
- Serle, Percival (1949). "Gruner, Elioth". Dictionary of Australian Biography. Sydney: Angus and Robertson. Retrieved 2008-12-30.