Lynch is born in Dublin on March 25, 1859. Her father, who is a committed, non-violent Fenian, dies when she is young. Her mother, Anna Theresa Calderwood, is married twice. She grows up in a very female house with her mother and ten sisters and half-sisters. Her stepfather is James Cantwell, also a Fenian, who runs the Star and Garter Hotel. After finishing school she works as a sub-editor for a provincial paper and as a governess in Europe.
A nationalist like her father and stepfather, Lynch is an executive member of the Ladies’ Land League and as a result closely associates with Fanny Parnell. She writes extensively, producing short stories and satirical sketches, as well as Land War fiction, travel writing, translations and literary criticism. Her satirical pieces include “A Dublin Literary Coterie Sketched by a Non-Pretentious Observer” (1888) and “My Friend Arcanieva” (1895). She publishes William O’Brien‘s paper United Ireland from France, after it is suppressed in Ireland. She disagrees with William Butler Yeats on the literary merit of Emily Lawless, calling her work “highly polished literary stories.”
Lynch also writes fiction on the subject of political and cultural affairs in Ireland, sometimes meeting controversy. Her first novel, Through Troubled Waters (1885), is a fictionalised version of a real-life incident in Galway in which the daughters of a prosperous landowning family are murdered to make way for the sons to inherit the land. The novel also depicts the rural clergy as complicit, by denouncing the victims from the pulpit. The newspaper United Ireland strongly criticises the novel, claiming it peddles in anti-Irish stereotypes for a British audience. She responds by stating that she had intended the book for an Irish publisher and audience, and that she should not be asked “to prove my patriotism at the expense of truth.”
Lynch publishes across Ireland, the United Kingdom and from Paris. By 1896, she has settled in Paris, having also lived in both Spain and Greece. She speaks Greek and French. She then returns to lecture in Ireland and is a part of the salons of Paris in the Belle Époque as well as the Irish Literary Revival in Dublin. She is friends with the historian, biographer and literary critic Arvède Barine (pseudonym of Louise-Cécile Vincens), the writers Mabel and Mary Robinson, and the medievalist Gaston Paris. Her work however does not bring significant income and she is forced to apply to the Royal Literary Fund for help on multiple occasions. Eventually it takes a toll on her health. She spends time in hospital in Margate in England in 1903.
Lynch dies in Paris on January 9, 1904.