Page then became Treasurer (finance minister) under Stanley Bruce. Although the title "Deputy Prime Minister" did not exist, the coalition agreement specified that Page would rank second in the ministry.
Professionally Dr Earle Page continued medically and on 22 Oct 1924 had to "tell his best friend", Thomas Shorten Cole the news that his wife Mary Ann Crane had just died on the operating table from complications with intestinal or stomach cancer - reputed by their daughter Dorothy May Cole to be "the worst day of his life".
The "Bruce-Page" government remained in power until 1929. He was a strong believer in orthodox finance and conservative policies, except where the welfare of farmers was concerned: then he was happy to see government money spent freely. He was also a "high protectionist": a supporter of high tariff barriers to protect Australian rural industries.
When the Bruce-Page government was defeated by Labor in 1929, Page went into opposition. In 1931 Joseph Lyons was able to form a UAP government without Country Party support. In 1934, however, the coalition was re-formed, and Page became Minister for Commerce. He was made a Knight Grand Cross of the Order of St Michael and St George (GCMG) in the New Year’s Day Honours of 1938. When Lyons died suddenly in 1939, it was Sir Earle whom the Governor-General Lord Gowrie called on to become caretaker Prime Minister. He held the office for three weeks until the UAP elected a new leader. While ten Australian Prime Ministers were knighted (and Bruce was elevated to the peerage), Page is the only one who was a knight at the time of becoming Prime Minister.
Page had been very close to Lyons, and he disliked Robert Menzies, Lyons's deputy, on the grounds that Menzies had been disloyal to Lyons. When Menzies was elected UAP leader, Page refused to serve under him, and made an extraordinary personal attack on him in the House, accusing him of cowardice for failing to enlist during World War I. His party soon rebelled, however, and Page was deposed as Country Party leader and replaced by Archie Cameron.
In 1940 Page and Menzies patched up their differences for the sake of the war effort, and Page returned to the Cabinet as Minister for Commerce. However, Page's charges were not forgotten and were occasionally raised in parliament by Menzies' opponents (notably Eddie Ward). In 1941, however, the government fell and Page spent the eight years of the Curtin and Chifley Labor governments on the opposition backbench. He was made a Companion of Honour (CH) in June 1942. In 1949 Menzies returned to office and Page was made Minister for Health. He held this post until 1956, when he was 76, then retired to the backbench.
Page was the first Chancellor of the University of New England, Australia, which was established in 1954. Earle Page College was formed in his honour as a residential college on campus, and is the venue for the Earle Page Annual Politics Dinner, which has had numerous prominent national and international guest lecturers.
Page refused to consider retirement from Parliament, even at the 1961 election, when he was 81, suffering from lung cancer and too sick to campaign. In one of the great electoral upsets of Australian history, he lost his seat, which he had held for 42 years. He had become comatose before the election, never regained consciousness, and died a few days later without ever knowing he had been defeated.
Page is the longest serving Australian federal parliamentarian who represented the same seat throughout his career. Only Billy Hughes served in Parliament longer, however Hughes represented four different electorates in New South Wales and Victoria.