After the 2014 Thai coup d'état, he served as an advisor to the military junta (National Council for Peace and Order, NCPO) responsible for drafting the post-coup 2014 interim constitution.

He continued his studies in the United States, completing his Master of Laws (1974) and Doctor of Juridical Science (1976) from the University of California, Berkeley.

Wissanu agreed and Thaksin made him deputy prime minister, responsible for legal and parliamentary affairs.

[8] Political scientist Eugénie Mérieau cites Wissanu Krea-ngam, along with Meechai Ruchuphan and Borwornsak Uwanno, as leading examples of legal scholars who laid the juridical foundations for authoritarian rule in Thailand, and as exponents of a "legal-military alliance for illiberal constitutionalism."

Wissanu, according to Mérieau, is a proponent of theories that legalised coups d'état "by reference to the continuity of the Thai state as embodied by the king".