On 10 February 1984, Mulock's strong performance and personal popularity led to him becoming Deputy Premier after the retirement of Jack Ferguson. He was opposed by both major ALP factions and Wran, his chief rivals for the job having been the left-wing Frank Walker and the right-wing Terry Sheahan. On the first ballot, Walker polled 32 votes, Mulock 20, and Sheahan 17. When Sheahan was eliminated from the contest, all but one of his preferences flowed to Mulock who was victorious by 36 votes to 33.