"The human rights movement in China and across the world has lost a principled champion who devoted his life to defending and promoting human rights, peacefully and consistently, and who was jailed for standing up for his beliefs," the United Nations High Commissioner for Human Rights, Zeid Ra'ad Al Hussein, said in a statement.
"Liu Xiaobo was the true embodiment of the democratic, non-violent ideals he so ardently advocated," Zeid added, also calling the 2010 Nobel Peace Prize winner "the definition of civic courage and human dignity."
Chinese officials ignored international pleas to let him spend his final days free and abroad.
Zeid also praised the Nobel laureate's widow, Liu Xia, who is being held by China under house arrest.
Zeid called on China to grant Liu Xia "freedom of movement, and allow her to travel abroad should she wish so.