A Brisbane couple whose generosity has transformed numerous charitable causes across Australia have revealed the personal motivations behind their extraordinary $40 million donation to Fight MND, the organisation established to support research into motor neurone disease (MND).

Quentin and Kylie Birt, who have donated more than $100 million to charities over the past two years, said they never intended to become known as philanthropists. Instead, they view their contributions as a simple opportunity to help where they can.

The couple's latest donation, announced during the Big Freeze event in Melbourne, was inspired by the work and legacy of Neale Daniher, the former AFL player and coach who became one of Australia's most recognised advocates in the fight against MND.

Mr Birt said reading Daniher's book and learning more about his determination to raise awareness and funding for research deeply moved both him and his wife.

"We said if we can do it, we will," Mr Birt explained, describing the decision-making process behind the donation.

Although the contribution became public knowledge, the Birts initially hoped to remain anonymous. Mr Birt said he viewed their gift no differently from smaller donations made by everyday Australians.

"A little kid that decides to save up bottle tops and donates $22 or whatever — you might consider it's the same," he said. "He's done what he could, and I've done what I could."

The couple's connection to MND extends beyond Daniher's advocacy. Mr Birt revealed that one of his employees died only weeks after being diagnosed with the disease, while another close friend had battled a similar degenerative condition.

"It's an awful thing," he said, expressing hope that future medical breakthroughs could eventually lead to effective treatments or a cure.

Now 86 years old, Mr Birt grew up on a dairy farm near Gympie in regional Queensland. Describing his childhood as "very poor," he became the first child in his district to attend high school before embarking on a career in engineering.

In 1973, he founded Q H & M Birt, a civil construction company that began with little more than a station wagon, a wheelbarrow and a shovel. Over the decades, the business expanded into one of Australia's largest civil construction operations, completing billions of dollars' worth of projects.

The Fight MND donation is just one example of the Birts' growing charitable involvement. In recent years, they have supported educational initiatives in Uganda and contributed $57 million to the Redtails Pinktails Right Tracks Program, designed to create sporting opportunities for Indigenous athletes in Central Australia.

Despite the scale of their giving, Mr Birt insists they are not driven by recognition.

"We're not wandering the planet trying to be philanthropists," he said. "It's what I want to do."

Their remarkable contribution to Fight MND stands as one of the largest charitable donations in Australian history and reflects the enduring influence of Neale Daniher's campaign to improve the lives of people affected by motor neurone disease.