The court on Friday ordered on a new presidential election to be held within 60 days, saying that the electoral board committed "irregularities and illegalities" during the vote.
Voters of opposition leader Raila Odinga have filled the streets of the capital, Nairobi, cheering their support for the court's decision
At the time of publication, #SupremeCourtDecides and #ElectionsKE2017 were the most popular Twitter hashtags in Kenya.
Many social media users tweeting on the issue said that the court's judgment was a victory for Kenyan democracy.
Last month's election is the first one to be nullified in the East African country.
"The declaration [of Kenyatta's win] is invalid, null and void," said Judge David Maraga, announcing the verdict of four out of the six judges.
Following the announcement, many took to Twitter to congratulate the judges for their decision.
According to the results announced by the electoral commission before they were nullified, Kenyatta had been declared the winner with 54 percent of the votes.
Some of his supporters also took to social media to express support for the leader of the Jubilee Party.
Source: Al Jazeera and news agencies