Colombia's Constitutional Court has ruled that President Alvaro Uribe can stand for re-election next year, overturning a single-term limit.
Opinion polls currently make the right-wing Mr Uribe a clear favourite.
Mr Uribe had argued for a change in the law, saying he needs four more years to implement his tough policies against Colombia's left-wing guerrilla groups.
Opponents of the move said allowing re-election in Colombia would give presidents too much power.
Mr Uribe is one of Washington's strongest allies in South America, where many governments have recently shifted to the left.
Judges took almost a month to reach the decision, after examining 18 challenges to the amendment.
"The court decided to declare as reasonable within the Constitution the legislative act allowing the re-election of the president of the republic," Constitutional Court President Manuel Jose Cepeda said.
The BBC's Jeremy McDermott in Colombia says there are fears that leftist guerrillas, who are desperate to avert another four years of Mr Uribe, will escalate a campaign of violence.
The president now has to wait for the court to approve a second law which will set out rules for sitting presidents running for re-election.
The decision is expected sometime in November.