An environmental campaigner who distributed a fake press release that caused a coal company's share price to crash has been released on a good behaviour bond.

Jonathan Moylan, from Newcastle, received a 20-month prison sentence after pleading guilty to disseminating false information, but Supreme Court Justice David Davies ordered his immediate release on a $1,000 bond.

Moylan distributed a fake statement to the media purportedly from the ANZ bank in January 2013, which said the bank was withdrawing $1.2 billion in funding from a Whitehaven Coal mine project in north-west New South Wales.

The false information was published by some media outlets and caused a temporary $314 million drop in Whitehaven Coal's market value before a trading halt was put in place and the hoax was revealed.

Moylan, 26, pleaded guilty to disseminating false or misleading information affecting market participation.

Supreme Court Justice David Davies said Moylan was "undoubtedly an intelligent person" but noted he had prior convictions and fines for "persistent offending", including trespassing.

He said he was convinced Moylan did not mean to harm shareholders and that his actions targeted ANZ and Whitehaven.

Justice Davies rejected Moylan's claim journalists were to blame for the share price plunge.

"The market was manipulated," he said.

He acknowledged Moylan's contrition, apology letter and early guilty plea, saying he was discounting the sentence by 15 per cent.

Moylan was supported at court by about 100 people, many holding signs that said: "I stand with Jonathan Moylan."

Australian Securities & Investments Commission (ASIC) Commissioner Cathie Armour said confidence in the integrity of the financial markets was "of the utmost importance".

"The capital markets are important to Australia, with many Australians owning shares either directly or indirectly, particularly through their superannuation funds," she said.

The maximum sentence Moylan could have received was a jail term of 10 years.