The 23-year-old was airlifted in a critical condition to the Alfred Hospital in Melbourne from Mafeking near Ararat, in the state's southwest, in the early hours of Sunday but later died.
Two other men aged in their 30s and 40s were reportedly also taken in a stable condition to East Grampians Health Service suffering suspected overdoses.
The Pitch Music and Arts Festival was subsequently cancelled due to dangerous heatwave conditions and extreme fire danger.
The Victorian Greens say the man's death should be a trigger for Premier Jacinta Allan to "shift gears and finally set up pill testing".
"While this Labor government continues to stall, young Victorian lives are being put at risk," party spokesperson Aiv Puglielli said in a statement on Monday.
"Even with pure MDMA we've seen how extreme heat can deal a deadly blow. So with untested drugs circulating, this was truly a disaster waiting to happen."
The Greens say if further overdose deaths are to be prevented, pill testing needs to be established onsite at music festivals as a matter of urgency.
"It's taking an already dangerous situation and turning it lethal."
State opposition leader John Pesutto said the death did not change the Victorian Liberals' position on pill testing.
"We need to do a whole lot more to raise education and awareness about the risks of this and ensure that festival hosts are doing their bit and meeting their responsibilities to make sure all of those safety procedures and plans are in place," he told reporters at Parliament House in Melbourne.
Mr Pesutto also attacked the state government for planning no media briefings for Monday.
"For Jacinta Allan and her government to hide when important issues need to be addressed, speaks volumes about the government and its lack of transparency."
AAP has contacted the Victorian government for comment.
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