She faces down the much larger bull, hands on hips, and was commissioned to highlight gender inequality.
But now a New York artist has taken a stand against the new arrival by adding a third statue - a urinating pug.
Alex Gardega's creation - now removed - took aim at the little girl's left leg.
He told the New York Post the Fearless Girl statue was "corporate nonsense" devised to promote the fund managers who commissioned it.
"It has nothing to do with feminism, and it is disrespect to the artist that made the bull," he said. "That bull had integrity."
He said he had consciously done a sloppy job on his dog statue, dubbed Pissing Pug, to reinforce his point.
"I decided to build this dog and make it crappy to downgrade the statue, exactly how the girl is a downgrade on the bull," Gardega said.
The sculptor removed his piece about three hours after installing it, saying he did not want it to be stolen - and did not have permission to leave it there.
But the pug's brief appearance generated a large and occasionally heated debate on social media.
Some felt that the urinating pug was offensive, delivering an anti-feminist message - while others agreed with the artist that Fearless Girl was not art, but a marketing ploy.
Some, however, simply lampooned the entire exchange between artistic types.
Arturo Di Modica, the Italian-born artist who created the bull, was dismayed by the appearance of the girl statue. He has argued that its presence changes the artistic meaning of his work.
Di Modica is now suing State Street Global Advisors, who installed the rival artwork, for trademark and copyright infringement.
The imposing bull sculpture appeared as guerrilla art in 1989, without any city permits.
It was meant to represent the "strength and power of the American people" in response to the market crash in 1987.
Gardega has had no contact with either Di Modica or Kristen Visbal, who made Fearless Girl.
Thus far, neither has commented on the canine interloper.
On the eve of International Women's Day in March this year, Wall Street's iconic Charging Bull statue was joined by a defiant little girl.