Somerville was born in Corfu; died at Castle Townshend, Ireland. She was brought up in her family's eighteenth century house in West Cork. Her upbringing provided her with much of her material for her writing. She trained as an illustrator, and studied art in London and Paris. Edith Somerville tried to adopt the pseudonym Guilles Herring, but it did not catch on.
She was a keen huntswomen and suffragist. In 1903 she was the first woman master of foxhounds, and from 1912 to 1919 she was master of the West Carberry Pack. She was also president of the Munster Women's Franchise League. She exhibited her work as an artist from 1920 to 1938.
She made at least one radio appearance reading her poetry in 1926. In later life she was a close companion of the lesbian composer Ethel Smyth.
Somerville and Violet Florence Martin were second cousins and met in 1886, after which they became lifelong companions and literary partners. They came to share a home in Drishane, County Cork.
They collaborated on a series of humorous novels about the rural Irish gentry. Their most important literary achievement was their novel The Real Charlotte (1894), in which the two main characters are cousins.
Some Experiences of an Irish R. M. (1899), is about a resident magistrate in Ireland. This was adapted for television in 1983-4 as The Irish RM, starring Peter Bowles.
The lives of the two women were dramatised by Maureen Duffy in her BBC radio play Only Goodnight (1981), in which Edith Somerville was played by Mary Wimbush and Violet Martin was played by Rosalind Adams.
In 1986 the BBC radio play The Irish Cousins: On the Hunt for Somerville and Ross also by Maureen Duffy was produced with Kate Binchy as Edith Somerville and Sorcha Cusack as Violet Martin.
After the death of Violet Martin in 1915 Edith Somerville continued to write under their joint literary names, the pseudonym Martin Ross, claiming that they were still in contact.
They left thousands of letters and 116 volumes of diaries detailing their relationship. Although they never explicitly described their relationship as lesbian they did make it clear that they regarded themselves as married.