Pillay has held human rights abusers and war criminals accountable for decades, following conflicts around the world that have left deep wounds.
During a press conference in Nuremberg, she also dedicated the prize to all those who have survived international crimes and to those who continue to defend international justice.
"We live in a time when international law and human rights are under political attack. This is particularly evident in the attacks on the International Criminal Court," Pillay said.
The 85-year-old received a standing ovation from her gathered colleagues.
You don't expect to be honored anymore when you're 85, which is my current age. But this is the highest honor bestowed upon me.
Investigating crimes in Gaza
The Norwegian Nobel Committee said that Navanethem “Navi” Pillay, with “exceptional courage and integrity (has) led the way towards a more cohesive global legal order.”
She emphasized that an international legal system in which criminals are held accountable and victims receive justice is a condition for peace.
Attempts to weaken international criminal justice and to jeopardize the progress made since Nuremberg risk throwing us back into a world where power rather than law determines whose suffering counts.
A year ago, Navi Pillay was involved in concluding that Israel's warfare in the Gaza Strip constituted genocide against the Palestinian population.
"We have concluded that genocide is taking place in Gaza and continues to take place, and the responsibility lies with the State of Israel," she said at the time, as one of three experts who had investigated the matter on behalf of the UN Human Rights Council (UNHRC).
Israeli Prime Minister Benjamin Netanyahu criticized the choice of laureate in a statement issued by his office, accusing the Nobel Committee of having "lost its moral compass." Netanyahu also claimed that Pillay had "spread blood libels against the world's only Jewish state."
“The decision is impartial”
Pillay lamented that the international legal system had been unable to stop what was happening in Gaza. The Nobel Committee does not explicitly mention the conclusions on Gaza, but Pillay did:
One of the big reactions to that report has been to praise my courage. Imagine my surprise: Why would it take courage to tell the truth? You interpret the law, you review the facts, and the decision that is made is impartial.
Israel denies all accusations of war crimes.
South African Pillay defended Nelson Mandela and his colleagues in their fight against the apartheid regime in her home country. After apartheid, she became a judge on the country's highest court - something she likes to emphasize.
But what she especially wants to highlight is her work to ensure that rape and sexual violence in conflict zones are now classified as crimes against humanity.
I am proud of that.
Born in 1941 in Durban, South Africa, to parents of Indian Tamil origin, she is an international law lawyer, judge and human rights advocate.
She played a key role as a lawyer during the apartheid regime, defending opponents of apartheid and criticizing the regime's interrogation methods.
She was a judge at the International Criminal Tribunal for Rwanda (ICTR) between 1995 and 2003, and its president from 1999.
She was the UN High Commissioner for Human Rights between 2008 and 2014.
She was a judge at the International Criminal Court (ICC) in The Hague between 2003 and 2008.
Particularly noted for her efforts to include rape and sexual crimes in the definitions of genocide and crimes against humanity, she concluded last year that Israel was committing genocide in the Gaza Strip.
Earlier this year, she was awarded the Olof Palme Prize together with her South African legal colleague John Dugard.
Today, she serves as a judge in the International Court of Justice (ICJ) case against the military junta in Myanmar.
