The public health agency announced the decision this week, saying the African leader will focus on
noncommunicable diseases such as heart attacks and strokes on the continent.
But Saturday morning, as public disapproval of the decision grew, WHO's director-general said in a tweet he was "rethinking the approach in light of WHO values."
"I'm listening," Dr. Tedros Adhanom Ghebreyesus wrote. "I hear your concerns."
Mugabe has long been criticized for corruption and abuse of power, and the decision to name him a goodwill ambassador for WHO stunned health experts and rights activists.
"The government of Robert Mugabe has brutalized human rights activists, crushed democracy dissidents and turned the breadbasket of Africa -- and its health system -- into a basket case," said Hillel Neuer, executive director of UN Watch, which monitors the performance of WHO, a UN agency that focuses on international public health.
"The notion that the UN should now spin this country as a great supporter of health is, frankly, sickening."
Tedros, an Ethiopian and WHO's first African director-general
, previously said Mugabe will use his role to ensure other leaders on the continent make noncommunicable diseases a priority.
"Zimbabwe ... places universal health coverage and health promotion at the center of its policies to provide health care to all," Tedros, who goes by his first name, said in making the announcement.
Zimbabwe has established a fund for noncommunicable diseases, "an innovative domestic resource mobilization approach that other countries can learn from," WHO tweeted.
At 93, Mugabe, one of Africa's longest-serving leaders, has ruled Zimbabwe since 1980 with little opposition.
Along with his inner circle, he has been under US sanctions since the early 2000s over human rights abuses and the erosion of democratic institutions. President Barack Obama extended sanctions for another year before leaving office in January.
In 2009, Mugabe's ruling party spent more than $250,000 on a lavish birthday party for the leader despite an ongoing food shortage and cholera outbreak in Zimbabwe.
Naming the leader a "goodwill ambassador for anything" is an embarrassment for WHO, Iain Levine, a deputy executive director at Human Rights Watch, said on Twitter.
What's a global ambassador?
Goodwill ambassadors for WHO are public figures
appointed to two-year terms by the director-general. They work closely with UN officials to raise awareness of global health issues.
Former New York Mayor Michael Bloomberg was named a global ambassador for noncommunicable diseases last year.
Health groups protest
More than 25 global health organizations that attended a conference in Uruguay,
where Mugabe was named a global ambassador Wednesday, signed a joint statement expressing shock and concern.
The organizations acknowledged that Mugabe has made commitments to fight noncommunicable diseases as a priority in his country but noted he has a long track record of human rights violations.
It's not the first time a UN appointment of the mostly ceremonial roles has raised eyebrows.
Last year, the United Nations stripped "Wonder Woman" of her role as a honorary ambassador for the empowerment of women and girls. Many UN workers protested
when the scantily clad comic book character was appointed a figurehead for the feminist campaign.