Guinness is born Hermione Maria-Gabrielle von Urach, the only child of the marriage of Albrecht von Urach, from Lichtenstein Castle, a member of the royal house of Wurtemberg, and Rosemary Blackadder (1901–1975) from Berwickshire in Scotland, a journalist and artist, who are married in Oslo, Norway in 1931. For the first few months of her life she is very ill. In 1934, her parents, both working as journalists, move the family to Venice. They later move again, to Japan. Her mother develops depression, and in 1937 tries to gain uninvited access to Emperor Hirohito‘s palace with her daughter. This results in her mother being arrested, sedated, and deported, which is the beginning of a decline in her mental health which culminates in a lobotomy in 1941 and spending the rest of her life in private mental institutions. Urach is returned to Europe, where she is raised by her godmother, Hermione Ramsden, in Surrey and Norway. She is educated by as many as seventeen governesses, with brief spells in boarding schools. Until the age of eighteen she is known as Gabrielle.
The couple moves to Ireland in 1955 where they rent Carton House, County Kildare. They share a love of Georgian architecture which results in them buying Leixlip Castle in 1958, and establishing the Irish Georgian Society on February 21 of the same year. Through the society they campaign for the restoration and protection of architectural sites such as Mountjoy Square, the gateway to the Dromana estate in County Waterford, the Tailors’ Hall in Dublin, and Conolly’s Folly in County Kildare. In 1967 they purchase Castletown House, also in County Kildare, with a plan to restore it, and make it a base for the Irish Georgian Society.
During the 1960s Leixlip Castle is a hub for those interested in architecture and conservation, and the Guinnesses work hands-on on a range of projects. By 1969, their marriage is in difficulties and Guinness moves to London. She later moves to Glenarm, County Antrim to live with Hugh O’Neill, and when that relationship ends, she returns to Leixlip Castle, but a divorce is finalised in 1981. Having lived in Dublin for a time, she rents Tullynisk House, the dower house of Birr Castle in County Offaly in 1983. Guinness becomes isolated and develops a problem with alcohol. While returning to Ireland from Wales on a car ferry on May 8, 1989 she has a massive heart attack which is compounded by a reaction to an injection of penicillin. She is buried at Conolly’s Folly.
Through Patrick, Guiness becomes grandmother of the fashion model Jasmine Guinness. Her daughter Marina is a patron of the arts and of Irish musicians including Glen Hansard, Damien Rice, and the band Kíla. Marina has three children of her own: Patrick (by Stewart Copeland of The Police), Violet (by photographer Perry Ogden), and Finbar (by record producer Denny Cordell).
In 2020, a new film on Guinness’s life and work, entitled Memory of Mariga, receives its United States premiere as part of the Elizabethtown Film Festival on Saturday, September 19, at the Crowne Pointe Theatre in Elizabethtown, Kentucky. In 2021, the same film receives its Irish premiere at the Fastnet Film Festival.