One of Sydney's most famous street murals will be preserved following a historic decision by the Marrickville Council to heritage list it.

It's a decision original artist Juilee Pryor calls "brave" and "extraordinary".

The "I Have A Dream" mural on King St in Newtown was created during a weekend in August 1991. Ms Pryor and Andrew Aiken, who later served a jail sentence in the UK for murder and now lives in Canada, had twice asked for permission to paint it but were refused. So they decided to do it anyway.

They decided the best way to conceal themselves was by hiding in plain view. Starting at 7pm on Friday night, they worked into the night and continued the next night. When they needed extra height, they borrowed a friend's cherry picker to finish the job. Ms Pryor described the experience as "wonderful".