Callum was born in Hamilton but his family returned to Gisborne when he was 2. He was educated in Gisborne (Elgin School, Gisborne Intermediate and Gisborne Boys High School), then studied a BBS - Accountancy extramurally through Massey University while working for McCullochs (now BDO Gisborne) before doing full time study in Palmerston North. He then moved to the audit team at McCullochs and completed secondments through their association with KPMG in New Zealand and Australia. Callum progressed to audit manager and has also specialised in Financial Reporting Standards, Charities Reporting, Livestock Taxation and the Emissions Trading Scheme.

Callum joined Graham & Dobson as Audit Manager in 2016, progressed to Associate in 2017, and then a Principal in 2018.  His area of focus is Audit with clients including Charities, Maori Incorporations, Incorporated Societies and other Not-For-Profit entities, along with providing financial consultancy services to local government and farming related entities.