The man is not thought to be linked to an earlier case of coronavirus at the mass gathering that saw thousands rally in support of the Black Lives Matter movement.
A second person who attended the Black Lives Matter rally in Melbourne has tested positive to coronavirus.
Victoria Health confirmed the person is one of 12 new cases across the state in the past 24 hours.
It is not thought to be linked to an earlier case of coronavirus at the mass gathering on Saturday, June 6, Victoria's Chief Health Officer Brett Sutton said.
The protester wore a mask at the demonstration and was not showing any symptoms, Mr Sutton said.
"He took a great deal of care in taking a distance from others," Mr Sutton said.
"It's very unlikely he acquired [the virus] there, he could have acquired it in a number of places."
Of the other new cases of COVID-19, seven are linked to a family outbreak in the suburbs of Coburg, Broadmeadows and Pakenham.
That includes four school children, two who attended St Dominic's School in Broadmeadows and two others at Pakenham Springs Primary School.
Both schools are closed today for on-site learning.
Of the remaining newly-identified cases, two are linked to a hospital patient, another is in hotel quarantine and the other is under investigation.
Source: 9News https://www.9news.com.au/national/coronavirus-victoria-records-12-new-covid-19-cases-school-outbreak-black-lives-matter-protester/e9afe494-85a9-4cbd-939f-f7fae1b58689