The election commission had declared incumbent President Uhuru Kenyatta the victor of last month's election. And again, I say peace. "That is the nature of democracy".
Worldwide observers had said they saw no sign of manipulation of voting and tallying at polling stations.
A lawyer for Kenyatta, Ahmednasir Abdullahi, said the decision was "very political" and the election board had "done nothing wrong".
Raila Odinga will feel vindicated against accusations that he was just being a bad loser in challenging President Kenyatta's win.
The run up to the vote was marked by court challenges over voting procedures and fears over the effectiveness and credibility of the IEBC, whose management was only appointed in January.
Raila Odinga celebrates the Supreme Court's decision with other National Super Alliance leaders.
Odinga, speaking after the ruling, called it "a very historic day for the people of Kenya and by extension the people of Africa".
Mr Odinga said Mr Chebukati and his team "belong to jail" while Mr Musyoka said that they have no faith in the commission.
President Kenyatta, in a televised address, said that it was "important to respect the rule of law even if you disagree with the Supreme Court ruling".
Now Odinga has another chance, though he still faces an uphill climb - Kenyatta's party swept the legislature and local elections, and the now-voided results put him 1.4 million votes ahead in August's vote.
"A declaration is hereby issued that the third respondent was not validly declared as the President-elect and that the declaration is invalid, null and void", the six-judge Bench led by Chief Justice David Maraga ruled.
The then commission headed by Issack Hassan was accused of bungling the 2013 General Election and corruption, including taking bribes from ballots printer Smith and Ouzman. Maraga said the alleged electronic hacking of the results had compromised the "integrity of the entire presidential election".
"If Nasa demands the removal of the IEBC, we will also remove all the Supreme Court judges", Mr Murkomen, who is poised to take the House Majority Leader slot, said.