Johan Arenas Rua was arrested in the northwest department of Antioquia, prosecutors said in a statement.
He is accused of acting as financial overseer of a gang called the Usuga Clan.
Arenas Rua served in the army from 2006 to 2008.
The drug gang stems from rightwing paramilitary groups that fought for decades in Colombia's 50-year-old war against leftist rebels, before disarming from 2003 to 2006.
Authorities say the drug ring has sent tons of cocaine to the United States and Central America.
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