Mario Uribe, a cousin and close ally of former Colombian President Alvaro Uribe, has been sentenced to seven and a half years in prison.
A former senator, Mario Uribe was found guilty of having links to the country's paramilitary groups.
The right-wing militias were created by landowners and drug traffickers to combat left-wing rebels.
He is one of the most prominent figures jailed over paramilitary links.
Mario Uribe, 61, who served as president of the Colombian Congress from 2001 to 2002, was found guilty of having ties with the United Self-Defence Forces of Colombia (AUC).
The AUC committed some of the worst mass killings in Colombia in the 1980s and 1990s as part of their campaign to combat left-wing guerrillas and anyone they suspected of being sympathisers.
As part of a 2003 peace deal, most paramilitary leaders surrendered and demobilised tens of thousands of their men in exchange for reduced jail terms and protection from extradition.
Around 70 former and current politicians are serving sentences for conspiring or collaborating with the paramilitaries, in what has been dubbed the "parapolitics" scandal.
Prosecutors said Mario Uribe had met AUC commander Salvatore Mancuso in 2002 to discuss how the paramilitaries could support his political campaign.
The Supreme Court said the paramilitaries had devised a plan to forge ties with politicians by financing their campaigns so they would gain allies in Congress.
The prosecution's star witness, a paramilitary best known as "Pitirri", said the AUC had also helped Uribe buy land at a reduced price.
Human rights groups say the paramilitaries forced farmers to sell their land at low prices by threatening them or driving them off their land.
Uribe has denied any involvement with the illegal groups, saying there were "zero paramilitaries" in his life.
Update 24 February 2011: An earlier version of this story said Uribe was also being investigated in connection with his alleged involvement in crimes against humanity committed by the paramilitaries. The president of the Supreme Court has since clarified that no investigation is taking place.