Australia's four largest consultancy firms have gifted hundreds of thousands of dollars to major political parties while securing millions of dollars in government work.

Australian Electoral Commission data released Thursday revealed Prime Minister Malcolm Turnbull was the country's biggest individual political donor last financial year. His $1.75 million contribution to the Liberal Party was more than three times bigger than the next largest: $500,000 from Roslyn Packer, the widow of media magnate Kerry Packer.

While Mr Turnbull's contribution helped bankroll the 2016 election campaign that returned the Coalition to government, it is only being formally disclosed now - 19 months after the election - because the money was paid after July 1, 2016.

Mr Turnbull gave $1 million in October 2016 and a further $750,000 two months later, before declaring the donation publicly a year ago.