Former Chilean President Michelle Bachelet, who took the helm of the UN human rights office on Monday, will need a strong voice in confronting populists and crises marked by war crimes, activists said.
Bachelet swiftly called on Myanmar to free two Reuters journalists convicted earlier in the day for their reporting on the crackdown on Rohingya.
Bachelet was chosen by United Nations Secretary-General Antonio Guterres to succeed Zeid Ra'ad al-Hussein of Jordan and the appointment was approved by the General Assembly last month.
She was tortured during the dictatorship of Augusto Pinochet but later rose to serve twice as Chile's president.
She inherits an inbox that includes conflicts in Yemen and Syria and crises in Venezuela and Nicaragua.
"This is an extraordinarily challenging time for human rights, given the rise of autocratic populists, the increasingly muscular hostility of China and Russia, the loss of the US and often the UK as voices for human rights, and a leadership void making possible a proliferation of atrocities in such places as Syria, Yemen, and Myanmar," Ken Roth, executive-director of Human Rights Watch, told Reuters.
But he said some governments and UN officials hope she will be "quieter and more selective" than Zeid who criticised governments in China, Israel, Russia and the United States.
The UN Human Rights Council, which opens a three-week session on Sept 10, is due to hold a debate on extending the mandate of its investigators on Yemen. It will also examine the next steps towards ensuring justice in Myanmar.
Another activist group, UN Watch, said last month that Bachelet has "a controversial record when it comes to her support for the human rights abusing governments who rule Cuba, Venezuela and Nicaragua, and we need to know how she plans to address these urgent situations."
Zeid, asked last week his advice to Bachelet, told reporters: "To very much continue along the same trajectory."