Álvaro Uribe, Colombia’s conservative former president who shaped the country’s politics more than anyone over the past 25 years, was found guilty on Monday of bribery in criminal proceedings and procedural fraud. It was the first major criminal conviction of a former Colombian leader.

Mr. Uribe was accused of working with a lawyer in an unsuccessful effort to bribe a former paramilitary to retract testimony that damaged him. The paramilitary had said that Mr. Uribe, 73, founded and financed a paramilitary group in the 1990s, during the country’s long and bloody internal conflict.

The ruling, by Judge Sandra Heredia of a lower circuit court in Bogotá, is likely to further divide the nation, which has long debated the legacy of Mr. Uribe’s role in the conflict. As president from 2002 to 2010 he pursued an aggressive military campaign against the country’s leftist rebel groups, significantly weakening the largest group and bringing a measure of security the nation had not seen in years.

But critics say his government’s tactics led to human rights violations against civilians and accused him of supporting right-wing paramilitary groups, for which they argue he should be held accountable.

The case has stretched on for 13 tumultuous years. Mr. Uribe has stated that he will appeal a decision that goes against him, a process that could take years and is likely to end at the Supreme Court.

This month, he called the case against him an “unjust judicial process.” He had argued that some judges were biased against him and illegally tapped his phone as a part of the investigation, but Judge Heredia found that the wiretapping was legal.