Ashoka Mukpo, 33, was working for NBC News and is being flown back to the US for treatment.
He had been hired on Tuesday to work with NBC News chief medical editor Dr Nancy Snyderman covering the outbreak which has so far killed more than 3,000 people in West Africa.
A statement on the news network’s website said; “The freelancer came down with symptoms on Wednesday, feeling tired and achy. As part of a routine temperature check he discovered he was running a slight fever. He immediately quarantined himself and sought medical advice.”
He went to a Medecins Sans Frontieres treatment centre on Thursday and a positive result for Ebola came back 12 hours later.
Mr Mukpo, who has been working in Liberia for three years, is the fourth American to contract Ebola in Liberia during the current outbreak. The others were Christian missionaries.
NBC News President Deborah Turness said: “We are doing everything we can to get him the best care possible. He will be flown back to the United States for treatment at a medical centre that is equipped to handle Ebola patients. We are also taking all possible measures to protect our employees and the general public.
“The rest of the crew, including Dr Nancy, are being closely monitored and show no symptoms or warning signs.
“However, in an abundance of caution, we will fly them back on a private charter flight and then they will place themselves under quarantine in the United States for 21 days.”
“We want to be respectful to our colleagues and the US public,” Dr Snyderman said. “Because we know this is not a casually transmitted disease and because we don’t have any symptoms, we present zero to minimal risk. Our returning to the US is a very, very minimal chance of getting anyone [else] sick.”