The 70-year-old Finnish composer Kaija Saariaho was regarded as a pioneer in classical music.
Her family reported that she had received a diagnosis of an aggressive form of brain cancer in 2021 but had chosen to keep it a secret so she could concentrate on her job.
An acclaimed violin concerto was among her early compositions, but it was her debut opera, L'Amour de loin, which gave her international recognition in 2000.
The film's director, Peter Sellars, praised her music for its "secret beauty.".
Her most recent opera, Innocence, did not premiere in the United Kingdom until April 2023 at the Royal Opera House.
It features a mass shooting, is sung in nine different languages, and is set at an international school in Helsinki.
Hush, her trumpet concerto, which was her last composition and will be performed for the first time in Helsinki, where she was born in 1952, was only just finished at the end of March.
She explained to the BBC last year how she was inspired by nature: "I was a very solitary child and I spent all the summers in my mother's home village on a lake that I loved the sound of. ".
She has discussed how she was mesmerized by the sounds of the wind, snow-covered feet, or waves and that this led her to local churches where she learned to play the violin, piano, guitar, and then the organ.
Her music had an endless life force, according to Peter Sellars, who directed many of her operas. It is unlike any other music in the world. Every performance is brand-new incredible," he said on BBC Radio 3.
Between Brahms and Haydn, she was ranked 17th out of the 50 greatest composers of all time in a BBC Music magazine survey last year.
At the Sibelius Academy in Helsinki in the 1970s, Saariaho studied under conductor Esa-Pekka Salonen and composer Magnus Lindberg. They had all benefited from Finland's national network of music schools and later founded a society called Korvat auki (Ears Open) in Finland that was devoted to modern music.
She eventually grew weary of being known as the sole female composer in Finland and relocated, first to Germany and then to Paris, where, in 1982, she enrolled in a computer music course at the renowned Ircam institute, which is known for its avant-garde aesthetic. .
Both male and female composers in Finland continue to look up to her.
Saariaho stated earlier this year that she still felt very Finnish in an interview with BBC Music Matters. "I really don't believe I ever left Finland. I tend to be very honest and direct. I don't enjoy debates and public speaking, and I believe French people engage in both activities frequently. ".
She made the acquaintance of Jean-Baptiste Barrière in Paris, whom she later married and worked with. She was in Helsinki when the Covid pandemic broke out in 2020, while he was still in Paris.
I will be apart from my husband for a longer period of time than ever before," she said at the time.
Her family said in a statement on Friday that her case should serve as a reminder of the plight of those with immunocompromised individuals. "Twice Kaija contracted Covid in public settings where insufficient precautions, if any, were taken to safeguard the most vulnerable among us. ".
The Orchestre de Paris paid Kaija Saariaho homage by saying that it was with great sadness that it learned of her passing because "we shared so many wonderful musical moments" with her.
According to the Royal Opera House, she was one of the most important composers of her time and had a significant influence on its audiences.
