In 1961, after the fall of the fourth government of Gaston Eyskens and the following snap election, Lefèvre became Prime Minister of a coalition government with the Belgian socialists. During this period, the Belgian army intervened in Congo (Operation Dragon Rouge). His government encountered heavy opposition and the planned health care reform only succeeded due to large concessions made by the government. Having become unpopular, Lefèvre lost the elections of 1965 and was excluded from the next government, which was a coalition government of Christian-democrats and liberals.