The death of the 84-year-old was confirmed by the Ferguson family in a statement released to the PA news agency on Friday afternoon.
She met Sir Alex met in 1964 when he was just 23 years old and they married shortly after in 1966. They have three sons Mark, born in 1968, and twin boys, Peterborough manager Darren and Jason, born in 1972.
United issued a statement on Friday which read: “Everyone at Manchester United sends our heartfelt condolences to Sir Alex Ferguson and his family on the passing of Lady Cathy, a beloved wife, mother, sister, grandmother and great-grandmother, and a tower of strength for Sir Alex throughout his career.”
Ferguson retired in 2013 after the death of Lady 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.”
Lady Cathy had previously talked him out of retirement in 2002.
At United, Ferguson won 13 Premier League titles, five FA Cups, four League Cups, two UEFA Champions League, one European Cup Winners Cup (defunct) one Intercontinental Cup and one FIFA Club World Cup.
He won the Scottish league at St Mirren (1976/77) and Aberdeen (197980, 198384, 198485).
In 1983, he led Aberdeen to beat Real Madrid 2-1 in the final for the European Cup Winners Cup.