Sereno, for her part, vowed to continue fighting against abuses of power and intimidation by Duterte's administration irrespective of the fact she has been removed from office.
She has been accused of failing to pay about two million pesos (£29,500) in taxes as well as falsifying and tampering with court resolutions.
The decision to oust Sereno without an impeachment trial has been described as "a legal abomination", by one of the Associate Justices who voted against today's move.
Even some allies of authoritarian President Rodrigo Duterte - who threatened to have Sereno fired because she criticized him - disagreed with the way she was ousted.
Police say about 1,800 protesters gathered by midmorning to support Sereno outside the court in Manila where anti-riot policemen blocked an access road with trucks and iron railings to maintain order.
The impeachment hearing against Sereno resumed at the House of Representatives.
"In this case, it was found that respondent is ineligible to hold the Chief Justice of the Supreme Court position for lack of integrity on account of her failure to file a substantial number of SALNs [Statements of Assets, Liabilities and Net Worth] and also, her failure to submit the requires SALNs to the JBC [Judicial and Bar Council] during her application for the position", Associate Justice Noel Gimenez Tijam wrote in handing down the decision.
Roque added that the Supreme Court was also duty-bound to uphold the Constitution.
"This is more than a wake-up call". However, court insiders said the voting was moved to May 11, simultaneous with the submission of the justices separate opinions on the case.
Marvic Leonen, one of the six who voted against removing Sereno, said the petition should have been dismissed outright.
Critics said the court's action set a unsafe precedent and would give the Duterte administration a legal weapon to curb and muzzle dissent.
The former law professor at the state-run University of the Philippines says the government petition that her fellow justices approved violated the constitution, which provides that top officials like her can only be removed by impeachment.
MALACAÑANG, which has been publicly at odds with Sereno, only said the public should respect the SC decision.
The decision came barely a day after Sereno announced on Thursday she was returning to work as the chief justice after she went on an indefinite "wellness leave" three months ago.
'The decision is immediately executory without further need of action from the court, ' Te said, adding the vote was 8-6 against Sereno. She was appointed later that year.
Duterte said he had avoided getting involved in efforts to remove Sereno but got fed up.
"I don't care about human rights, you better believe me", he said. But there are still some lawmakers calling for the impeachment to proceed independently from the Supreme Court.
The House Justice Committee said in March there was probable cause to impeach Sereno, accusing her of corruption, breach of public trust and other serious crimes.
Duterte's spokesman released a statement saying: 'The High Court has spoken.
Sereno has denied any wrongdoing.
The Philippines lived under martial law a generation ago, when dictator Ferdinand Marcos used military rule to suppress his critics.