His rival, Raila Odinga, and others had alleged that massive fraud, including tampering with results forms, had taken place.
The 55-year-old will be sworn in as the country’s fifth president next week.
The eight petitions challenging the elections were all dismissed. The court found some were based on forged documents and “sensational information”, Chief Justice Martha Koome said in a unanimous decision on behalf of the seven judges.
No credible evidence that the electronic voting transmission system had been tampered with by “a middle man” was presented, she said.
Ms Koome also said that Mr Ruto had met the constitutional threshold of garnering 50%+1 of votes cast.
The ruling ends a protracted election dispute that started after polls closed last month.
Mr Odinga’s team had used the dissent of four of the seven electoral commissioners – who disowned the poll results because they had fallen out with the chairman – to bolster his case.
But the court, while noting the “dysfunction” of the commission in managing its internal affairs, said it was not convinced that the claims of the chairman running a one-man show was enough to undermine the election.
“Are we to nullify the outcome of an election on the basis of a last-minute boardroom rupture whose details remain scanty?” the judges asked
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