The Animal Justice Party has secured the final spot in the NSW upper house, potentially thrusting issues such as puppy farms, battery egg farming and the high rate of animal euthanasia onto the political agenda.

While the government will only need the support of Fred Nile's Christian Democratic Party to pass most legislation through Parliament, it may be forced to negotiate with new Animal Justice MP Mark Pearson on issues the CDP does not support.

Mr Pearson, currently the executive director of Animal Liberation Australia, said he was thrilled by the result. He starts his new job on Monday.

"It's time to go shopping for suits. In the animal rights movement you don't often wear a suit when you're doing investigations and rallying for animals," he told Fairfax Media.

Mr Pearson, 55, lives in Newcastle and formerly worked in mental health. His parents instilled in him the need to "consider animals and consider those who can't advocate for themselves, who don't have a voice we understand".

He will lobby MPs to reject a proposed crackdown on animal rights activists who trespass on farms to gather video evidence of animal cruelty.

He will also seek to have battery cages for hens banned, and to address perceived cruelty in the kangaroo meat trade.

Mr Pearson will also fight against hunting in national parks, the high rate of animal euthanasia in pounds and greyhound racing.

With the click of a computer mouse on Friday, an official from the NSW Electoral Commission set in motion a complex calculation that distributed preferences on millions of ballot papers to determine the result.

The 21st and final spot had been a race between No Land Tax, the Animal Justice Party and the Liberals. ABC election analyst Antony Green said the result was "possible, but I didn't think it was going to happen".

He said it meant the Greens preference flow to the Animal Justice Party was about 15 per cent.

"It shows that if parties encourage people to direct preferences under optional preferential voting, people actually do that," he said.

The result heads off a potential legal challenge by Animal Justice to the election result. An early hiccup with the state's electronic voting system, iVote, meant the Animal Justice Party and Outdoor Recreation Party were left off the "above the line" section of the ballot paper for two days of voting.

About 19,000 votes were cast before iVote was suspended and the problem, which was due to human error, was fixed.

The Animal Justice and Outdoor Recreation parties had both signalled a legal challenge. However, Peter Jones of the No Land Tax party has reportedly also threatened to challenge the result. Mr Jones alleges that Liberal Party election workers told No Land Tax workers they would not be paid, and that they should leave their posts.

However, a successful court challenge to the result by No Land Tax is considered highly unlikely. The upper house, or Legislative Council, comprises 42 MPs who serve eight years terms. At each election, 21 MPs face election.

Most pieces in the final upper house jigsaw puzzle were already in place after earlier counting. It gave the government nine seats, Labor seven, the Greens two and one each to the Christian Democratic and Shooters and Fishers parties.

The upper house battleground was almost as vital for the government as the lower house at last month's election, because the Coalition needs a working majority to pass its reforms, including its controversial power privatisation plan.

To pass laws in the last parliament, the government required the backing of the Shooters and Fishers Party, which shared the balance of power and has vowed to block the electricity privatisation plan.