"If something isn't fair, what are you going to do to make it fair?" she challenged those attending a graduation ceremony at the Dunedin Town Hall on Saturday.
"To be good citizens you must hang on to your sense of what is just.
"You must believe that you have a personal responsibility to try to change those things that are not just," she said.
"Each of you can contribute to changing the world in which you will live, if you bring to it your energy, intelligence and determination and an unswerving commitment to justice, compassion and the strong sense of values that is part of the fabric of this university."
It was the first in a series of six graduation ceremonies, including two in Invercargill, being run by the university this month.
Ms Sewell, who is also the chief executive of the Ministry of Education, noted that on February 23, 1997 a lamb called Dolly had been born in Scotland, having been cloned from an adult cell.
That this could have been done was "amazing" and 50 years ago would have seemed "miraculous".
"It opens up all sorts of possibilities for cures for genetic defects in humans and plants but it also confronts us with significant ethical issues.
"Today's technologies have the power to change our lives and we, in our humanity, have the power and the responsibility to use these technologies in ways that will sustain and protect our world and those who live in it."
Knowledge was expanding at a "breathtaking pace".
It was estimated that in the years from 1999 to 2002 the amount of new information produced approximately equalled the amount produced in the entire history of the world up to that time.
Accordingly, effective education could no longer be focused "just on the transmission of pieces of information that, once memorised, constitute a stable storehouse of knowledge".
She noted that Charles Dickens had begun his novel David Copperfield by asking "Whether I shall turn out to be the hero of my own story, or whether that station will be held by anybody else, these pages must show."
Graduates faced the same question.
"Don't wait for others to act. Be the hero of your own life."
She also urged graduates to have the confidence to "take on most difficult questions and problems and to offer responsible, principled and creative answers".
"We want you to be good citizens; responsible to and for the communities in which you will live.
"We need you to care about and stand up for what is good in our world and to recognise and change what is wrong."
