"It's a coup," she told reporters, speaking publicly for the first time since senators voted to begin an impeachment trial against her.
It took Brazil's Senate about 20 hours of debate to reach a decisive result early Thursday: The country's first female President must step aside while the trial gets underway.
It took Rousseff less than an hour to make two speeches slamming the vote: One to reporters inside the presidential palace and one to crowds outside after she was kicked out.
"I'm the victim of a great injustice," Rousseff told cheering supporters.
She delivered a fiery speech from a podium set up outside, stopping several times to ask people around her to move so she could see the crowd.
She shook hands with onlookers, kissed a baby and hugged people afterward.
All the while, she decried the impeachment proceedings as a betrayal and an injustice. The effort, she argued, is the latest in a string of moves by her opponents since she took office.
"My government was the target of nonstop sabotage," Rousseff said. "The objective was to stop me from governing and therefore allow an environment inviting the coup."
Rousseff is accused of breaking budget laws, but she maintains she did the same things previous Brazilian leaders have done.
"I have made mistakes, but I have not committed any crimes. I am being judged unjustly, because I have followed the law to the letter," she said.
Later, as acting President Michel Temer
addressed the nation on television, several dozen Rousseff supporters attempted to force their way into the presidential palace in Brasilia. The protesters were repelled by police who used pepper spray to disperse the crowd.
"I am convinced that it is necessary to rescue Brazilians' trust internally and internationally," Temer said. "Because it is fundamental so that our companies and workers, therefore all the productive areas within the country, can have enthusiasm and go back to their secure investments."
Temer said he had wished the handover ceremony could have been discreet and sober then realized he should say a few words to the people of Brazil.
He also said he had "institutional respect" for Rousseff.
The acting President said Brazil must be united to move forward.
"We don't have a lot of time. We have to be committed so we can implement the reforms that the country needs," he said.
President says she'll keep fighting
Rousseff vowed to keep fighting efforts to impeach her, and called for her supporters to join her.
"Destiny has reserved many challenges for me. ... Some of them seemed impossible to overcome. I have suffered from torture, I have suffered from sickness, and now I suffer from the pain of injustice," she said. "What is more painful now is injustice. I am victim of a political farce. But I won't give up. I look back and I see all we have accomplished. I look forward and I see all we still need to do."
The past few months have been a roller coaster for the embattled leader. And while there are some procedural steps we know are coming, given the country's volatile political landscape, what will happen next is anyone's guess.
This much is clear: Rousseff will be suspended for up to 180 days. That means she could be on the sidelines, fighting for her political future, when the Olympics come to Latin America's largest country in August.
As Rousseff spoke, Temer, her one-time vice president, posted a photo on his official Twitter account of the moment when he took power.
Rousseff retains her title as President by law, but she will not be fulfilling the duties of that office.
Speaking through the night, senators made their cases in a marathon session ahead of the electronic vote. Fifty-five of the 81 members of the upper house voted in favor of the motion early Thursday, with 22 voting against.
The senators were each given 15 minutes to speak, with a buzzer indicating when their time was up. Seventy-one of the house's 81 members took the opportunity to have their voices heard.
Former President Fernando Collor de Mello, himself impeached by the Senate in 1992, said he feels the country has "regressed politically."
His colleague, Armando Monteiro, said the impeachment was politically motivated and will set a dangerous precedent.
"We will, indeed, be promoting a rupture in the nation's institutional order."
As the senators put forward their views, protesters in Brasilia, the capital, and in other cities demonstrated for and against the proceedings. Some of the protests -- like the one in front of Congress in Brasilia -- got out of hand, prompting authorities to disperse the crowds.
"It is revolting, we are here defending our democracy, and those yes-men spray us with tear gas, they are cowards," said one protester, Celma Pereira, a teacher.
Olympic dreams shattered
The spell on the sidelines could put Rousseff out of commission when her country hosts the Olympics in August, a showcase event that she's worked on with her predecessor since Brazil won its bid for the Games.
The International Olympic Committee said Thursday that it remains confident the Summer Olympics will be a success.
"There is strong support for the Olympic Games in Brazil and we look forward to working with the new government to deliver successful Games in Rio this summer," officials said.
A special Senate committee will now investigate the accusations against Rousseff. Once that committee is done -- which could be as late as November -- her team will have 20 days to present her defense. After that, the committee will vote on a final determination and then present it for a vote in the full Senate.
It will take a two-thirds majority to remove the President from office.
No matter how long the proceedings take, Thursday's carefully choreographed exit for Rousseff made it clear she's already making her case in the court of public opinion.
After she finished her speeches Thursday, she posted a video on YouTube
, titled "Democracy is the right side."
Why was the motion against Rousseff considered?
Corruption allegations have been dogging Rousseff's administration since 2011.
A sweeping investigation into a multimillion-dollar kickback scheme at the state-run oil company Petrobras embroiled dozens of the country's leading businessmen and politicians. While she isn't accused directly of profiting, Rousseff was the chairwoman of Petrobras during many of the years of the alleged corruption.
In December, a bid to impeach Rousseff was launched by the then-speaker of the lower house of Congress, Eduardo Cunha, who argued that the President was guilty of breaking budgetary laws by borrowing from state banks to cover a shortfall in the deficit and pay for social programs in the run-up to her 2014 re-election.
She has also been blamed for the worst recession since the 1930s, now in its second year.
Sen. Waldemir Moka told the upper house during his allotted time that, if the impeachment trial is successful, the future president will assume a government with a 250 billion Brazilian Real debt ($72.5 billion) according to conservative projections, with the possibility of that being up to 600 billion Real ($174 billion).
Why is Brazil in such a mess?
Along with the precarious state of the Brazilian economy -- the country faces a crippling recession that has left hundreds of thousands unemployed and thousands of businesses closed, while inflation has gone through the roof -- the country faces a number of other, high-profile challenges, from dealing with the Zika virus to a fraught 2016 Olympics, which are due to open in Rio de Janeiro in August.
That's if they even open. One doctor, Amir Attaran of the University of Toronto, says the risk of the virus in the city is too great, and has urged authorities to postpone or relocate the event in an effort to curb the spread of the epidemic.
Meanwhile, Brazil soccer legend Rivaldo has said the country is getting "more ugly" and has warned visitors to "stay away
," citing the violence in the city.
Whatever happens, it is unlikely to be an entirely smooth process. Rousseff's supporters have vowed to take to the streets in retaliation, ensuring a long, and potentially messy, battle ahead.