CANBERRA (Reuters) - Outspoken mining magnate Clive Palmer is set to play a key role in Australia's new Parliament after his start-up party won a third Upper House seat on Wednesday, giving him the power to block or pass laws.

His Palmer United Party could be crucial when conservative Prime Minister Tony Abbott, who won last month's election, tries to pass his reforms, including the abolition of a carbon tax and mining tax, through Parliament.

The self-described billionaire and resort owner, who plans to build a replica of the Titanic, formed the Palmer United Party less than a year ago after quitting his membership of Mr Abbott's Liberal-National Party alliance.

Election results on Wednesday confirmed his party will share the balance of power in the Senate with five other cross-benchers, who are mainly conservative leaning.

"The Palmer United Party looks forward to working with the Abbott government to get Australia back on track," Mr Palmer said in a brief statement.

In the past week, Mr Palmer has threatened to block all government laws unless the new government funds more political staff for his party, although he strongly supports Mr Abbott's plans to scrap the carbon and mining taxes.

A spokesman for Mr Abbott said the Prime Minister would work cooperatively with all new senators.

Mr Palmer is also edging closer to winning his Lower House seat of Fairfax after finishing just seven votes ahead of his nearest rival after the preliminary count of more than 89,000 votes.

Mr Palmer is a colourful character who attracts headlines. He once accused the American Central Intelligence Agency of plotting with the Greens, but later admitted he was just seeking publicity.

He lists "litigation" as among his hobbies, and made headlines in 2010 when he gave away 55 Mercedes Benz cars and 700 overseas holidays as Christmas bonuses to staff at his Queensland Nickel refinery.

Those elected to the Senate on Sept 7 will take their seats from July 1, 2014, when Mr Abbott's government will need support from six of the eight cross-benchers to guarantee a majority.

Mr Palmer's three Senators will be joined on the crossbenches by anti-gambling Senator Nick Xenephon, the socially conservative Democratic Labor Party and the Family First party, the conservative leaning Motorist Enthusiast Party and the Liberal Democratic Party.

Until next July, the Labor Party and Greens will control an upper house majority where they are likely to stall Mr Abbott's plans to quickly scrap the carbon and mining taxes.

Mr Palmer also faces a potential conflict of interest if he wins his Lower House seat and he will have to publicly declare his personal financial interests.

Voting rules for the lower house also ban a lawmaker from voting on issues where they have a direct financial interest, which could prevent Mr Palmer from voting on the abolition of the mining tax. Mr Abbott, however, has a clear majority in the Lower House and won't need Mr Palmer's vote.

Senate voting rules, however, place no restrictions on voting, even if there is a financial conflict, and Mr Palmer's party would be clear to vote to abolish the 30 per cent tax on iron ore and coal mine profits.

"There is nothing to stop any senator from voting on anything," former Senate Clerk Harry Evans told Reuters.