 The family emigrated to New Zealand in 1911.Educated at Whangarei High School, Brainsby went on to study at Auckland University College, graduating with a Bachelor of Arts in 1934, and a Bachelor of Laws and Diploma of Journalism in 1938.On 23 March 1940, Brainsby married Mary Priscilla Wrightson at St Aidan's Church in the Auckland suburb of Remuera, They adopted a daughter in 1957 and divorced in 1960.