Andres Felipe Calle was kidnapped in the northern town of Curumani while doing mapping for the Colombian geological service (SGC) on June 29.
On Tuesday he was released in good condition in the city of Aguachica, about 100 kilometers (60 miles) south of where he was captured, said Cesar Bohorquez, president of the police anti-kidnapping and extortion division.
SGC had reported that Calle, a professor at the University of Caldas, was detained alongside a student who was released several hours later.
The student said that they had been kidnapped by individuals identifying themselves as members of the ELN.
The Colombian government has opened preliminary peace talks with the National Liberation Army, or ELN, which is Colombia's second-largest rebel group.
The rebels are known for sabotaging the country's electrical, oil and mining infrastructure, among other acts of violence.