United Nations secretary-general Antonio Guterres designated the role to Ms Yousafzai at UN headquarters in NY and described her as a "symbol of perhaps the most important thing in the world, education for all".
Guterres also cited Yousafzai's "courageous defense" of the rights of all people, including women and girls, to education and equality, and honored her for showing "an unwavering dedication to peace" even in the face of great danger, and her desire to foster a better world.
Malala said she was honoured to be the Messenger of Peace.
Ms Yousafzai, who narrowly avoided death in 2012 after being shot by the Pakistani Taliban for campaigning for girls' rights to an education, is the youngest ever Messenger of Peace.
The deadly attack on the young girl sparked global outrage, and she was transferred from a hospital in Pakistan to Birmingham's Queen Elizabeth Hospital for life-saving treatment.
Malala became the youngest-ever Nobel laureate in 2014 when she was recognized for her advocacy of the right of all children to education.
This is published unedited from the IANS feed. Girls often lack access to education because they have to work, care for younger siblings or are married early.
Beyond issues of education, Yousafzai has also been an outspoken advocate on issues of conflict and refugees.
"And I realized that if you remain silent, you are still going to be terrorised".
After being shot, she was flown to a hospital in Birmingham, England, for treatment. But prayers are not enough. "We don't believe in anything that they're doing", she said.
While she is controversial among some in her home country - there are many who believe a number of different stories about her shooting, for example, that it was an American conspiracy - others believe she has helped advance education for girls.
"I'm a Muslim and I'm proud to be a Muslim..." She was designated the role at a ceremony in NY on Monday. "And, once you educate girls, you change the whole community, the whole society", Yousafzai said.
"It is our responsibility, especially in the richest countries, to express our solidarity to all those who unfortunately can not provide to their children the education they have the right to receive", he continued.
People drawn from the arts, entertainment, sports, science and public service are appointed Messengers of Peace, each with special missions. Others Messengers of Peace include usa actor Leonardo Di Caprio, Brazilian writer Paulo Coelho and U.S. singer Stevie Wonder.