Milligan is the eldest of eleven children born to Methodist parents Seaton Milligan (1837–1916) and Charlotte Burns (1842–1916), with nine surviving including Alice Milligan and Edith Wheeler. All nine children enroll at Methodist College Belfast which provides a privileged and exceptional education. She studies classical piano and composition at the Royal College of Music in London and the Conservatoires of Frankfurt and Milan. Following her marriage to Charles Eliot Fox in 1892, she settles in London.
In 1904 Fox co-founds with Alfred Perceval Graves the Irish Folk Song Society, an offshoot of the Folk-Song Society formed in 1898. Its aim is to collect and publish Irish airs and ballads, in addition to holding lectures and concerts on the subject. She acts as the society’s honorary secretary. The rules of the Society are collected in volume 4 of the Journal of the Irish Folk Song Society. The subscription is 5 shillings payable every January and committee meetings are held at the Rooms of the Irish Literary Society in London.
Fox is a musician in her own right and tours Ireland collecting folk songs and airs. She undertakes a series of tours of County Antrim between 1909 and 1910 with her sisters Edith Wheeler and Alice Milligan. The sisters record and transcribe songs by Irish singers, then publish articles and musical scores in The Journal of Irish Folk Song.
In 1910 Fox visits the east coast of the United States where the New York branch of the Irish Folk Song Society is formed. “The Bardic Recital” is produced on March 16 at the National Theatre in Washington, D.C. She collects and arranges the music for the play.
Fox rediscovers Edward Bunting‘s papers, and under the provision of her will they come to Queen’s University Belfast in 1916. From these papers she writes The Annals of the Irish Harpers. The publication of The Annals of the Irish Harpers stimulates a revival of interest in both the Irish harp and Edward Bunting. Alice Milligan nurses her sister prior to Fox’s death in London on March 25, 1916. An obituary of Charlotte Milligan Fox is in The Irish Booklover (1916). The Journal of the Irish Folk Song Society (1917) has a poem in remembrance of Charlotte Milligan Fox. The same issue has a memoir of Fox by Alice Milligan and an appreciation of Fox by Alfred Perceval Graves.
During 2010 and 2011, the Ulster History Circle mounts plaques for famous Ulster figures. Charlotte Milligan Fox and Alice Milligan have a plaque mounted on Omagh Library, 1 Spillar’s Place, Omagh, County Tyrone.