Greig started his career in operations with the New Zealand Dairy Board and moved into project delivery overseas.

He moved back to New Zealand in 2007 and has been consulting ever since. In that time he has gained considerable experience managing projects across multiple sectors including dairy, food and beverage, pharmaceuticals, water and wastewater, chemicals, power, oil and gas, and renewable energy.

Greig has been on the New Zealand Board of IChemE since 2009, and has been Honorary Treasurer since 2012. He represented New Zealand on Congress from 2018 to 2022.