Barrow won the 4 December poll with 53% of the vote. Runner-up Ousainou Darboe, who got about 28%, and two other candidates refused to accept the results, citing alleged problems at polling stations without providing evidence.
Darboe's United Democratic party (UDP) petitioned the Supreme Court to nullify the results the following week despite election observers having said the poll was conducted fairly.
The court dismissed the petition on Tuesday on the grounds that Darboe's party had failed to serve Barrow within five days of filing it, which violated the Gambia's fair trial procedures, judicial sources said.
"The UDP failed to comply with the requirement of Rule 11 of the Election Petition Rule, which required that you file a motion of petition and security," Chief Justice Hassan B. Jallow wrote in the judgment.
Neither Darboe nor his party could be immediately reached for comment.
Supreme Court decisions in the Gambia are final and cannot be appealed.
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