Who else made the 2018 Time magazine list?
Among those featured are:
*A group of Florida students who have been campaigning for gun control following the Parkland school shooting
*Hugh Jackman, actor
*Greta Gerwig, actress and director
*Guillermo del Toro, director
*Justin Trudeau, Canadian prime minister
*Robert Mueller, US special counsel
*Xi Jinping, president of China
*Leo Varadkar, Irish Taoiseach (prime minister)
*Emmerson Mnangagwa, president of Zimbabwe
*Shinzo Abe, prime minister of Japan
*Emmanuel Macron, president of France
*Jennifer Lopez, musician and actress
*Christopher Wylie, Cambridge Analytica whistleblower
*Virgil Abloh, fashion designer
*Oprah Winfrey, TV presenter
*Jeff Bezos, founder and CEO of Amazon
*Elon Musk, entrepreneur
*Sonia Friedman, West End and Broadway theatre producer
Brown, whose parents are British, has 2.2 million followers on Twitter and 16 million on Instagram.
In July last year she used her large social media reach to launch an anti-bullying campaign.
She tweeted encouraging messages to fans who had shared their stories of bullying.
After Time announced the list, Brown's fans praised her inclusion on social media.
For a girl of her age to "have so much maturity" is "pretty incredible", one person said on Twitter.
Weekly news magazine Time is read by millions of people around the globe.
It is perhaps best known for its prestigious "Time Person of the Year" award which first began in 1927 as "Man of the Year".
Past recipients have included Queen Elizabeth II and Mark Zuckerberg as well as, controversially, Adolf Hitler in 1938.
In his tribute to Prince Harry for this year's Time 100 list, singer Elton John said it has been a "joy" to see Harry "grow to inherit his mother's warmth, sense of humour and courage to stand up and champion the causes he truly believes in".
"Prince Harry has that rare ability to walk into a room full of strangers and make everyone feel comfortable and at ease," the performer added.
Rihanna features in the Icons category, with her blurb written by none other than Adele.
"She has designed and conquered an entire lane of her own," Adele wrote.
"The innovative and groundbreaking world of Rihanna that no one else will ever be safe in and get away with copying. She makes her own rules and bends ours."
The Barbadian singer has nine Grammys and has sold more than 18 million singles in the UK.