The Ferguson family confirmed the news in a statement released to the PA news agency on Friday afternoon.
“We are deeply saddened to confirm the passing yesterday of Lady Cathy Ferguson, survived by her husband, three sons, two sisters, 12 grandchildren and one great-grandchild,” the statement read.
“The family asks for privacy at this time.”
Cathy had been married to Sir Alex since 1966, with the couple having met while they were both working at a typewriter factory.
Ex-United manager Ferguson retired from the game in 2013 following the death of Cathy’s sister, Bridget.
He said at the time: “My wife Cathy has been the key figure throughout my career, providing a bedrock of both stability and encouragement. Words are not enough to express what this has meant to me.”
The couple have three sons, Mark, Jason and Darren, the latter of whom followed his father into football management and currently takes charge of League One side Peterborough.
A statement from United read: “Everyone at Manchester United sends our heartfelt condolences to Sir Alex Ferguson and his family on the passing of Lady Cathy.
“Lady Cathy was a beloved wife, mother, sister, grandmother and great-grandmother, and a tower of strength for Sir Alex throughout his career.”
Peterborough wrote: “Everyone at Peterborough United Football Club offers our sincere condolences to Darren Ferguson and his family on the passing of his beloved mother, Lady Cathy.
“We will support Darren during this incredibly sad time.”