WA mining magnate Andrew 'Twiggy' Forrest and wife Nicola on Monday made the largest living donation by any philanthropist in Australian history, announcing a contribution of $655 million to their Minderoo Foundation.

The donation brings the couple's total givings to the charity to $1.5 billion, and will go towards causes such as stopping plastic entering the oceans, eliminating modern slavery, fighting cancer, and - closer to home - helping with early childhood development in regional WA.

Philanthropists Andrew and Nicola Forrest. Credit:Andrew Meares

Asked what motivates them to donate so much of their earnings to charitable causes, Ms Forrest said she believed as country people, it was "part of their DNA" to help where they could.

"We both grew up in the country, and we both grew up where communities pulled together when there was any hardship," she said.