Arguably one of the first superstar players of the modern era, Keegan joined the club from Southampton just a few years after being named European Player of Year for two successive seasons while at Hamburg.
During a stellar career, he amassed 63 international caps for England and scored 21 times for the Three Lions.
He retired as a player in 1984, playing his final competitive game for United against Brighton before a friendly against Liverpool at St. James' Park days later - famously leaving the pitch in a helicopter while in full kit.
He sensationally returned to St. James' Park as manager in 1992 following the dismissal of Ossie Ardiles and after steadying the ship in the second tier, he would take the club on a spectacular journey over the next five years.
After gaining promotion to the Premier League for the 1993/94 season, United became one of the leading forces in the top flight, with a fearless attacking style seeing the team dubbed the Entertainers during the 1990s.
During that period, the Magpies finished as runners-up in the Premier League in both the 1995/96 and 1996/97 seasons - losing out by a narrow margin on each occasion to Manchester United.
The Magpies' dramatic 4-3 loss at Liverpool - where Keegan was also a player - in April 1996 is widely regarded as the Premier League's greatest ever game.
After departing in January 1997, he returned as manager between January and September 2008.