He graduated with Master of Arts and Bachelor of Music degrees, both with first class honours, and also taught composition, instrumentation and fugue.
He studied advanced conducting at the Guildhall School of Music and Drama having received post-graduate scholarships and graduated with the Ricordi Conductors' Prize.
While working in London, he also had the opportunity to compose incidental music for a number of theatre productions including scores for the Royal Shakespeare Company.
During the 1980s, he was a regular broadcaster on Radio New Zealand, presenting programmes on many aspects of music and on diverse composers such as Wilhelm Stenhammar, Erich Wolfgang Korngold and Aram Khachaturian.
A recording of Southgate conducting the NZSO in the orchestral music of Douglas Lilburn was released on the Continuum label.