"I am disturbed by the recent increase across the political spectrum in several states in Western Europe of a discourse rooted in anti-immigrant and racist sentiment and religious intolerance," Pillay told diplomats as she opened a UN Human Rights Council session in Geneva.
Following the stunning gains by eurosceptic, anti-immigrant and xenophobic parties in last month's European Parliament elections, she said politicians who have made a range of disturbing statements will figure among EU lawmakers.
The UN High Commissioner of Human Rights, making her last statement to the council, also noted that Marine Le Pen, who heads France's National Front (FN), will sit in the parliament, despite comments comparing "peaceful Muslim street prayers to the military occupation of her country by the Nazis".
And one of the new Italian MEPs has been found guilty of "setting fire to the pallets of migrants sleeping under a bridge," she said.
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"There is a road to perpetration of human rights violations. And hate speech - particularly by political leaders - is on that road," she said.
She highlighted the deadly attack last month on the Jewish Museum in Brussels, insisting that such acts of violence "are not unconnected to this climate of extremism".
"Expressions of racial, religious or xenophobic division that overtly call for, or suggest, targeted actions against minority groups should be anathema in every member state of the United Nations," she said.
She called on countries to implement human rights education campaigns to "counteract these alarming trends".