The New South Wales Government will introduce urgent legislation to validate past findings by the state's corruption watchdog, Premier Mike Baird says.

The announcement follows a successful High Court challenge to the powers of the Independent Commission Against Corruption (ICAC) brought against it by NSW crown prosecutor Margaret Cunneen.

The ICAC said the High Court decision narrowed its powers significantly and undermined some previous corruption findings, including those made against Travers Duncan and three other businessman relating to dealings with former Labor minister Eddie Obeid over a mining lease.

Mr Baird said the High Court decision should not "provide those who have done the wrong thing in the past with a loophole".

"All previous findings of corruption by ICAC should, and will, stand," he said.

"We will introduce a bill to that effect immediately."

Mr Baird said the Government would also commission an immediate review of the High Court decision and report back by July 10.

He said confusion over the ICAC's jurisdiction needed to be resolved.

"At the time those [previous] cases were done, there wasn't an issue of jurisdiction that was raised," Mr Baird said.

"That has obviously entered the debate more recently."

The review, which will be chaired by former High Court chief justice Murray Gleeson, could be followed by more new legislation, Mr Baird said.

Luke Foley said he was happy to work with the Premier to usher urgent legislation through the Parliament. ( ABC News: Brigid Glanville )

"We obviously reserve the right to take additional actions, which is fully expected post this review," he said.

The review will consider the appropriate scope for the ICAC's jurisdiction, any legal measures required to provide ICAC with the power to expose serious corruption and whether those powers should be limited or enhanced.

"I think what we've shown is that we have a zero tolerance approach," Mr Baird said.

Opposition Leader Luke Foley has backed the measures as a good first step towards ensuring the ICAC remains strong.

"I believe that the Premier is genuine when he says that he wants the state to have a strong Independent Commission Against Corruption," he said.

"To that end, I'm happy to work with the Premier to usher legislation through the Parliament as a matter of urgency."

However, one of the businessmen who stood to benefit from the High Court ruling, John McGuigan, criticised the proposed legislation as a "mockery of the judicial process".

The ICAC had indicated it would consent to an application to overturn a corruption finding against Mr McGuigan after the ruling.

Mr McGuigan said the Government's move to uphold all previous ICAC findings was "totally at odds with the legal principles embodied in the rule of law and the separation of powers".

"The High Court in Cunneen did not reveal 'a loophole', but rather determined the proper scope and extent of ICAC's powers," he said in a statement.

"For the NSW Government to now overrule the determination of ICAC's powers and scope of authority ... eliminates the ability of a citizen to protect his rights and rely on the judicial system to determine the proper scope and application of legislation."

The legislation will also validate the actions of the ICAC in recent inquiries relating to the Australian Water Holdings company and political donations to the Liberal Party.

However, Mr Baird said it would be up to the ICAC to decide whether to wait until the review is complete before handing down its findings in relation to those matters.

'Eager beavers' take place in 56th NSW Parliament

Mr Foley said his team would be a "far stronger Opposition" in the new term of Parliament after dozens of freshly elected MPs were sworn in today.

A tri-service honour guard prepared to greet Governor David Hurley on his arrival to open the 56th NSW Parliament. ( ABC News: Brigid Glanville )

Labor has 34 Lower House MPs after the March election, while the Coalition has 53 MPs and the Greens have three.

Two independents will also sit in the Lower House of the 56th NSW Parliament.

Mr Foley is among those who have taken their place in the chamber for the first time after he left the Upper House and successfully ran for the seat of Auburn.

"Good news for the Labor Party - 20 eager beavers, new Labor MPs, bursting with enthusiasm to represent their communities and Labor is back in the game in Macquarie Street," he said.

"We'll be a far stronger opposition holding Mr Baird and his colleagues to account for the great many promises they made to the people of New South Wales and emerging over the time of this Parliament as a credible alternative government, with an eye to forming government at what is now a very winnable election in 2019."