The 16-year-old from Sweden has become a prominent face in the fight to save the environment from the effects of climate change.
The magazine revealed its choice on TODAY Wednesday, making Thunberg the youngest selection since TIME began naming a Person of the Year in 1927. The Person of the Year title is not necessarily an honor or award, but representative of the influence the person has had on the news within the past year.
"She became the biggest voice on the biggest issue facing the planet this year, coming from essentially nowhere to lead a worldwide movement," TIME Editor-in-Chief Edward Felsenthal said on TODAY Wednesday.
Last year, TIME editors selected "The Guardians and the War on Truth," a group of four journalists and one news organization whose work landed them in jail or cost them their lives.
Thunberg, who was nominated for a Nobel Peace Prize in March, has been the catalyst in a host of student-led strikes involving more than a million students across the world in the last two years after she began spending her school days protesting climate change outside the Swedish parliament.
"She embodies youth activism," Felsenthal said. "Her rise in influence has been really extraordinary. She was a solo protester with a hand-painted sign 14 months ago. She's now led millions of people around the world, 150 countries, to act on behalf of the planet, and she's really been a key driver this year taking this issue from backstage to center."
She drew worldwide notice for her fiery speech at the United Nations Climate Action Summit in September after she sailed from England to New York in a solar-powered boat for the conference instead of flying because it's harmful to the environment.
Related: Teen climate activist Greta Thunberg
"This is all wrong. I shouldn't be up here,'' she said during her speech. "I should be back in school, on the other side of the ocean. Yet you all come to us young people for hope. How dare you!
"You have stolen my dreams and my childhood with your empty words. And yet I'm one of the lucky ones. People are suffering. People are dying.
"Entire ecosystems are collapsing. We are in the beginning of a mass extinction, and all you can talk about is money and fairy tales of eternal economic growth. How dare you!"
Her speech went viral, drawing praise from environmental activists and a mocking reaction from President Donald Trump.
TIME editors chose Thunberg over a shortlist of five candidates that also included Trump, Speaker of the House Nancy Pelosi, the anonymous CIA whistleblower whose complaint played a central role in triggering the impeachment proceedings and the pro-democracy protesters in Hong Kong.
"(Thunberg) also represents a broader generational shift in the culture that we're seeing from the campuses of Hong Kong to the protests in Chile to Parkland, Florida, where the students marched against gun violence, where young people are demanding change urgently,'' Felsenthal said.
Other candidates considered for the distinction included Facebook CEO Mark Zuckerberg, Chinese leader Xi Jinping, U.S. soccer star Megan Rapinoe, President Trump's personal lawyer Rudy Giuliani and New Zealand prime minister Jacinda Ardern.
The TIME editors also announced winners of four additional categories instead of designating runners-up for Person of the Year.
"Instead of runners-up this year, we are looking at people who dominated their sector, who influenced their field,'' Felsenthal said.
Disney CEO Bob Iger was named Businessperson of the Year after the successful launch of the streaming service Disney+ and a record of more than $10 billion in box office receipts for Disney films.
TIME also named "Public Servants" as the Guardians of the Year, which included the anonymous CIA whistleblower and "all of the career public servants who took great professional risks in pursuit of the truth." That group also included Marie Yovanovitch, Bill Taylor, Fiona Hill and Alexander Vindman, all of whom are current or former government officials who have played a role in the impeachment proceedings.