The couple’s children have said the couple died “peacefully and under circumstances of their own choosing” on Friday at a Zurich clinic run by the group Dignitas.
“After 54 happy years together, they decided to end their own lives rather than continue to struggle with serious health problems,” said a statement from the couple’s son and daughter, Caractacus and Boudicca.
The statement said Downes, who became Sir Edward in 1991, had become almost blind and increasingly deaf. His wife, a former dancer, choreographer and television producer, had devoted years to working as his assistant. It was reported that she had been diagnosed with cancer.
Downes’s manager, Jonathan Groves, said he was shocked by the couple’s deaths, but called their decision “typically brave and courageous”.
London’s Metropolitan Police force said it had been notified of the deaths, and was investigating.
Born in 1924 in Birmingham. Downes studied at Birmingham University and the Royal College of Music.
In 1952 he joined London’s Royal Opera House as a junior staffer – his first job was prompting soprano Maria Callas. He made his debut as a conductor with the company the next year and went on to become associate music director. He retained close ties to the Royal Opera, conducting 49 different operas there over more than 50 years.
He also had an decades-long association with the BBC Philharmonic Orchestra, where he became principal conductor and later conductor emeritus.
Their children said their parents “both lived life to the full and considered themselves to be extremely lucky to have lived such rewarding lives, both professionally and personally”.
The family said there would be no funeral.