Australia has officially joined the Trans-Pacific Partnership (TPP), a massive trade deal that the federal government says will deliver a windfall to farmers and businesses.

Prime Minister Scott Morrison confirmed Australia ratified the TPP on Wednesday, making it the sixth country to come on board.

The step means the TPP will come into effect on December 30.

The deal strips 98 per cent of tariffs for 11 countries with a combined GDP of more than $13.8 trillion and close to 500 million consumers.

Australia is forecast to get annual economic benefits of up to $15.6 billion from the deal by 2030.

Legislation enabling Australia to join the TPP cleared parliament earlier this month, after the pact was signed in March.

Australia follows Canada, Japan, Mexico, New Zealand and Singapore in ratifying the TPP, which also involves Brunei Darussalam, Chile, Malaysia, Peru and Vietnam.

The deal almost fell over when the United States pulled out, but Japanese Prime Minister Shinzo Abe and then-prime minister Malcolm Turnbull resurrected it.

“This is a great and enduring achievement for free trade in the face of a rising tide of protectionism in many countries,” Mr Turnbull tweeted.

“Thanks especially to @AbeShinzo – we resolved to get this deal done in Sydney nearly two years ago as we walked around the cliffs at South Head.”

Labor backed the legislation for the TPP despite raising concerns it needed stronger labour market testing and could allow foreign companies to sue the government.

The opposition was forced to defend its support for the agreement, which sparked internal tensions and angered the union movement.

-AAP