Sydney's brutalist landmark, the Sirius building, will remain standing for now, after the acting judge of the Land and Environment Court, Simon Molesworth, ruled that former heritage minister, Mark Speakman, made errors of law when deciding not to list the building on the State Heritage Register.

Justice Molesworth found that Speakman made errors when he considered that listing the building would cause financial hardship to the building's owner, Property NSW, and that he did not properly consider the heritage significance of the building.

Last year, Speakman rejected the Heritage Council's recommendation to protect the building, because "whatever the heritage significance of the building" is, that is outweighed by the "undue financial hardship" its listing would cause. Speakman said that by heritage listing Sirius, the building's sale value of an estimated $70 million would be reduced.

The decision was greeted with cheers in the courtroom, largely from those who have been campaigning to save the brutalist building, which was designed by Tao Goders and opened in 1980.

The Sirius was to have been demolished to make way for a new development, funds from which would be used to fund new public housing.

Read more about the Sirius:

Government puts social housing ahead of Sirius preservation

Brutalist landmark awaits heritage decision

CFMEU joins fight to save Sirius