Activist group GetUp's court victories create the opportunity for a major shake-up of electoral laws, including automatic enrolment of voters at 18, argues UNSW's Anthony Mason professor of law, George Williams.

The developments will have a profound effect on the electoral system, Professor Williams writes in the Sydney Morning Herald.

"In the short term, an extra 100,000 people are now entitled to vote. In the longer term, the judgments will help drive major electoral reform."

Professor Williams says the obvious answer is to move to a system of automatic enrolment using information already provided to government.

"The idea is being looked at in NSW and elsewhere and should be adopted nationally," he writes.

"It would require our electoral commissions to do the work of putting people on the roll when they turn 18 and keeping their details up to date. With 1.4 million Australians missing from the electoral roll and so unable to vote, it represents a sensible next step in the evolution of our electoral system."

To read the full opinion piece go to the SMH website.