The 50-year-old, who has vowed to make European integration the mainstay of his administration, will become the third president of an independent Ukraine, taking over after 10 years of authoritarian-leaning rule by outgoing leader Leonid Kuchma.
"The court has concluded that the complaint should not be granted," the Supreme Court ruling said on an appeal filed by defeated candidate, former prime minister Viktor Yanukovich.
"The decision is final and cannot be appealed," the chief presiding justice Anatoly Yarema said.
Basis of ruling
Aljazeera's Moscow correspondent Akram Khuzam, reporting from Kiev on the ruling, said the court made the decision after scrutinising a number of reports.
It was clear that the defeated candidate, Viktor Yanukovich, tried to prolong the term of the current authority for obvious reasons.
It was also clear that the last stage of the elections was by and large fair comparing with the previous rounds. Thus, it was obvious that the top court would take the decision it took.
Yushchenko will have to tread a
fine line in relations with Russia
According to Khuzam, as the winner, Viktor Yushchenko has to first deal with Russia as 60% of the Ukrainian economy basically depends on relations with Moscow. Hence, any tension in relations with Russia will not be in his favour.
A key plank of Yushchenko's electoral platform was to take Ukraine into the European Union, Khuzam said.
Thus, it is certain that relations with the West will be on the top of Yushchenko's priorities.
Khuzam added that ties with the United States also will be a key part of his presidential agenda. After all, many observers say the US spent vast sums of money to help Yushchenko win the election re-run.
The ruling frees parliament to set a date for Yushchenko's inauguration.
His swearing-in will cap months of political turmoil and uncertainty that have dogged the former Soviet nation.
The court said Yanukovich had not proven his charges that the 26 December re-run election that Yushchenko won by more than 2.2 million votes was marred by widespread irregularities and should therefore be annulled.
The same court ordered the repeat election nearly two months ago, after it threw out a November runoff won by Yanukovich because of electoral irregularities.