Geraldine Mucha was born in London on the 5th July 1917. She was fortunate to belong to a family with a strong musical background. Her father, Marcus Thomson, was a popular Scottish concert baritone and a professor of singing at the Royal Academy of Music in London. Her mother enjoyed success as a singing-actress and appeared in several notable London musical productions. Sir Thomas Beecham and Dame Edith Evans were among the friends that Geraldine remembered visiting her parents' home.
The precocious Geraldine was able to read music long before she could read words. She was encouraged to compose by her father and given lessons in harmony by his colleague, the composer Benjamin Dale. Later she was introduced to Sir Arnold Bax, who showed a keen interest in her ability and would often play through her compositions and discuss them with her. "He always took my music seriously", she recalled. After leaving school Geraldine gained a place to study composition and conducting at the Royal Academy of Music. Here she was able to continue her tuition with Benjamin Dale, also being taught by the composers Alan Bush and William Alwyn. Alwyn is said to have remarked, "that girl has so much talent you don't know if she's got a brain or not."
With Antony Judd as fellow pianist, Geraldine gave a performance of her first ballet Nausicaa at a student concert. When this score was later shown to Constant Lambert, conductor for Sadler's Wells Ballet, he was, "impressed, but sceptical that a woman could have written it." When the war began in 1939 the Royal Academy remained open but Geraldine was obliged to combine her studies with work on a telephone switchboard. However, she was able to compose incidental music for an anti-fascist play, which was well received, and to make musical arrangements for the BBC. In 1941, Geraldine met a young man in French uniform in Leamington Spa. He turned out to be the writer and war correspondent, Jiří Mucha, son of the famous Czech Art Nouveau painter, Alphonse Mucha. Before long the young couple were married and had set up home in a flat behind Marble Arch. With a key left under the mat, their flat became a refuge for any stray serviceman or poets, such as Dylan Thomas, that Jiří met on his travels. The couple returned to Prague in the autumn of 1945. Rafael Kubelik, the conductor, was a neighbour and soon became a good friend. Geraldine became involved in helping with the first Prague Spring Festivals. She gave suppers after the concerts and her guests included such notable musicians as Leonard Bernstein, David Oistrakh and Yehudi Menuhin. In 1950 Jiří was imprisoned by the Communists because he had been employed by the BBC during the war. Geraldine and their young son, John, lived in the country subsisting on a smallholding. After Jiří was released in 1953 the family returned to Prague and moved into the apartment which was to become their home for the next sixty years. In order to help their finances Geraldine worked for a music publisher as an editor and translator but she managed to write her own music too, "in order to keep me sane." As a member of the Czechoslovak Composers Union, Geraldine was given access to orchestral performances. Although these were infrequent, she was able to hear her piano concerto, suites and overtures played by orchestras such as the Czech Philharmonic and the conductor, Karel Sejna. The piano concerto and a suite from the ballet Macbeth were also recorded and issued by Supraphon.
Marriage to her bohemian husband proved neither easy nor conventional. For Jiří to be able to leave Czechoslovakia, Geraldine moved back to Great Britain so that he was permitted occasional "marital visits." From her cottage in Scotland, the couple were then able to travel the world organising exhibitions of the work of Alphonse Mucha. To the flower-power generation of the swinging sixties Mucha's graphics came as a revelation and proved to be immensely popular. Despite the great amount of extra work this involved, Geraldine still found time to compose. She wrote many works for a broad range of small ensembles, amongst them nonets, string quartets, a sonata for violin and piano, a wind trio, a piano trio, duos, and a wide variety of vocal pieces and songs. She was particularly fond of the "brilliant colours" of the woodwinds. In the early seventies she wrote several pieces for the soprano, Jill Gomez, some of which were broadcast by the BBC. Although some of her chamber music continued to be played, Geraldine's utter lack of professional ambition led to her orchestral works becoming neglected.
After the fall of the Iron Curtain she was once more able to make Prague her permanent home. Despite her retiring nature, Geraldine became a well-respected and much-loved figure and entertained visitors from all over the world – musicians, diplomats, and art-lovers – in her apartment near the castle. Here, surrounded by the family collection of artifacts and furnishings from Alphonse's Paris studio, she generously dispensed tea to those eager to hear her stories of the great painter and designer. Although she herself never met him (he died shortly after interrogation by the Gestapo in 1939), Geraldine was able to recount many vivid details passed on to her directly by the painter's wife, Maruška. Though Geraldine continued to work regularly at her compositions, modesty prevented her from drawing anyone's attention to the manuscript paper that was often open on her desk or propped on the piano. As she passed eighty, then ninety, friends and well wishers began to arrange occasional public performances of her chamber music, and respected Czech soloists asked her to write small pieces for them. Geraldine died on the 12th October 2012. Only two weeks earlier she had attended a special concert of some of her orchestral music given in honour of her 95th birthday. Following Jiří's death in 1992, Geraldine and her son, John, established the Mucha Foundation, to publicise and preserve the work of Alphonse and Jiří. The Mucha Foundation now also oversees Geraldine's archive and promotes her music.