Mackintosh was born in Cardiff, Wales and began full-time ballet training at the age of 18 after gaining a scholarship from the Buckinghamshire Education Committee.
[1] He trained at the Arts Educational School in London for three years, during which he took roles in pantomimes, toured Hungary with West Side Story in 1965 and took part in the BBC's John Cranko production of Onegin in 1966.
Prompted by the arrival of Rudolf Nureyev on the London scene, he travelled to New York to train with David Howard, Stanley Williams, Maggie Black and Valentina Pereyaslavec.
[2] Mackintosh commented in 2017 that "Rudolf's charisma and technical brilliance not only changed negative perceptions about male dancers, he spurred me to higher achievements.
"[3] He first visited South Africa in 1967, on David Poole's invitation, to debut as Prince Siegfried in Swan Lake.