After the 2014 Thai coup d'état, Borwornsak was appointed member of the National Reform Council (NRC), serving as this body's deputy speaker. At the same time, he chaired the junta-appointed Constitution Drafting Committee. However, in September 2015, the draft was rejected by a majority of the NRC members, resulting in a dissolution of both the drafting committee and the NRC itself. Borwornsak was replaced by Meechai Ruchuphan as chairman of a new Constitution Drafting Committee. In August 2017, Prime Minister Prayut Chan-o-cha appointed him chairman of the Legal Reform Committee.