The 6-3 vote Tuesday restored the suspended Basescu to power and invalidated claims made by rival Prime Minister Victor Ponta and his center-left coalition, saying the ballot question was based on outdated census figures, EUobserver.com reported.
Slightly more than 46 percent of registered voters cast ballots on the referendum, which didn't meet the required 50 percent plus one minimum, the court said. Of those who did vote, 87.5 percent voted to impeach Basescu.
"We stated that the referendum quorum condition was not met," court President Judge Augustin Zegrean told reporters Tuesday.
Romania's interim president, Ponta ally Crin Antonescu, told reporters he would stand down in compliance with the court ruling, EUobserver.com said.
While Basescu can return as president, he remains unpopular for having backed wage cuts and tax hikes for a $25 billion rescue deal struck with the International Monetary Fund, the European Union and the World Bank in May 2009.