Mr Wood, whose wealth was estimated at $372 million in last year's BRW Rich 200 list, gave $1.6 million to fund the Greens' TV advertising campaign, helping to significantly increase votes for the party in key states.

The donation easily surpasses the previous record for a single private political donation, a gift of $1 million to the Liberal Party during the 2004 election by a conservative British politician, Lord Michael Ashcroft.

Mr Wood's donation enabled the Greens to run advertisements on high rotation on commercial television stations for the first time. Independent market research found the ads had contributed to higher swings to the Greens in the states where the ads were run most frequently. The donation will be officially listed in the Greens' annual return, released by the Australian Electoral Commission next month.

Mr Wood has emerged as one of the country's leading philanthropists in recent years. He gave $8 million to the University of Queensland, where he studied, and $15 million to establish its Global Change Institute.

His private Graeme Wood Foundation holds about $20 million in assets and gives away about $1 million a year to a range of arts, youth and environmental causes - including helping fund the purchase of 27,000 hectares of Tasmanian native forest from the timber giant Gunns last year.

Four years ago Mr Wood stepped back from his executive duties at wotif.com, the online travel company he founded in 1999, but he remains a director and retains a 23 per cent stake in the company, valued at $222.24 million based on yesterday's closing share price of $4.63.

Speaking exclusively to the Herald before the release of the Greens' campaign figures, Mr Wood said his donation was motivated by disappointment with Labor and Coalition policies on climate change and the environment.

''I didn't think either of those parties were being effective,'' he said. ''They were being driven by people with vested interests.''

Helping the Greens to secure the balance of power in the Senate was a ''critical step'', he said. The Greens' vote tended to drop away in the final weeks of an election campaign as the bigger parties outspent them on advertising, and in May Mr Wood approached the Greens' leader, Bob Brown, to propose that he help fund a ''proper'' Greens ad campaign.

In the end, Mr Wood provided the bulk of the campaign funding. Mr Wood denied that he, or wotif.com, had anything to gain from his donation.

''There's nothing in it for me financially,'' he said. ''I'm not looking for any favours.''

Senator Brown said he would be ''forever grateful'' for Mr Wood's donation, which was both selfless and hazardous.

''There's nothing that Graeme could possibly gain personally out of this,'' he said, including influence over policy. ''Not ever has Graeme said 'I'd like you to do such and such','' he said.

It was a historic election result for the Greens, transforming it from a minor party to the third party in Australian politics. In both houses of Parliament the Greens secured the highest vote achieved by a third party since World War II, including the Democrats' best results, in 1990, and the Democratic Labor Party decades earlier.

The Greens' Senate vote rose much more in states where their ads played in higher rotation - particularly South Australia (6.8 per cent); Queensland (5.5 per cent); Western Australia (4.7 per cent) and Victoria (4.3 per cent) - than in states where there was less investment, particularly NSW, where the swing was less than 2 per cent because there was not enough money to cover the biggest state.