From 1947 to 1949 he was Under-Secretary to the Prime Minister. He was appointed by Peter Fraser to oversee the government's post-war state housing scheme. In 1951 he was nominated to stand for the deputy leadership of the party, but he declined the nomination. Moohan was a critic of Nash's leadership and helped organise a leadership challenge against him in 1954, though in the event switched sides and voted for Nash due to the increasing unpopularity of a leadership change among party members.