[2] He was the youngest son of Charles Nicholson Macintosh, newspaper editor and mayor of Timaru in 1901, and his wife, Lydia Beatrice Thompson.

[2] After the war, Macintosh trained at Guy's Hospital Medical School, qualifying MRCS LRCP in 1924 and FRCS Ed in 1927.

[3] In 1936, the University of Oxford approached Lord Nuffield to consider endowing three chairs in medicine, surgery, and obstetrics and gynaecology.

[3][4] In the Second World War, Macintosh held the rank of Air Commodore and trained anaesthetists for the armed services.

His research included hazardous experiments to test life jackets (immersing Edgar Alexander Pask in a wave tank while anaesthetised), the provision of respirable atmospheres in submarines and survival during parachute descent from high altitudes.