Shortly after the proclamation of Indonesian independence, Sumanang co-founded the National Press Company (Badan Usaha Penerbitan Nasional). In 1946, the Indonesian Journalists Association was founded, and Soemanang was elected as its first chairman. He further founded the daily newspaper Nasional (today Bernas) in Yogyakarta in November 1946, in addition to the magazines Wanita Indonesia and Revue Indonesia, and Javanese-language pamphlet Biwara.
