Emery Collins was a Cabinet minister in the government of Henderson Dewey. Sobel doesn't say which Cabinet post he held, although it was likely a senior one such as Minister for Foreign Affairs. Sobel notes that like Dewey's other appointees, Collins was articulate and popular, and like Dewey himself was able to present an appearance of modesty, understatement, and coolness, and appeared to great advantage on vitavision.
After Dewey's unexpected death on 10 May 1929, Collins was apparently not in the running to succeed him as leader of the Liberal Party. It is reasonable to assume that he supported his colleague Douglas Watson for the party leadership, since Watson chose Collins to succeed him as Minister for Home Affairs after being elevated to Governor-General.
During Watson's grand tour of Europe in April 1933, Collins presided over Cabinet meetings in Watson's absence, and Watson was in constant contact with him and the rest of his government. Collins presumably continued as Home Minister for the rest of Watson's term in office.