The New Zealand PM announced that she would never say the name of the attacker, as a way of denying him the infamy he sought when he carried out the Christchurch mosque shootings on Friday.
Ms Ardern has vowed to change the country's gun laws, help pay the funeral costs of the victims, and says she will refuse to say the gunman's name so as to deny him notoriety – instead encouraging people to "speak the names of those who were lost rather than the name of the man who took them."
London mayor Sadiq Khan tweeted a photo of Ms Ardern hugging a Muslim woman and pointed to how the prime minister, when in London last year, had talked about "the importance of inclusivity and equality in society."
Conservative MP Nick Boles called her refusal to name the attacker "tremendously powerful".
Adil Ray, a British actor and TV presenter, said he was "really impressed" with Ms Ardern for her "swift, strong leadership".
Cihangir Islam, a Turkish lawmaker from an opposition party, also praised Ms Ardern on Twitter, saying that she "says to Muslims in pain, 'You, you're us!' She symbolically covers her head when she goes to a home for condolences; she boldly underlines her respect and solidarity. How thirsty we have become for justice and mercy in state administration".
Faiza Ali, a community organiser, justice activist, and founder of the Muslim Democratic Club of New York, said on twitter: "Among the many faces & stories I'll remember from the #ChristChurchMosque tragedy, I will never forget Prime Minister Jacinda Ardern. What a remarkable leader."
Donald Trump has not publicly commented on Ms Ardern's response to the attack, instead criticising the "Fake News Media" and what he called its "ridiculous" attempts to blame him for the attack.
A trial shall be held in early April for the attacker.
