Robert Gordon Menzies was born to James Menzies and Kate (née Sampson) in Jeparit, a town in the Wimmera region of northwestern Victoria, on 20 December 1894. He was the fourth of six children, with one sister and three brothers. His father James was a storekeeper and held agencies for farm machinery and stock agents, the son of Scottish crofters who had immigrated to Australia in the mid-1850s in the wake of the Victorian gold rush. His maternal grandfather, John Sampson, was a Cornish miner from Penzance who also came to seek his fortune on the goldfields, in Ballarat. His father was elected to the Victorian State Parliament for the seat of Lowan in 1911 and moved with the family to Melbourne after selling the farm. One of his uncles, Hugh Menzies, had been a member of the Victorian Parliament for Stawell for two years up to 1904, while another uncle, Sydney Sampson, had represented the Division of Wimmera in the House of Representatives. His cousin, Sir Douglas Menzies, became a justice of the High Court of Australia He was proud of his Highland ancestry – his enduring nickname, Ming, came from /ˈmɪŋəs/, the Scots – and his own preferred – pronunciation of Menzies. His middle name, Gordon, was given to him in honour and memory of Charles George Gordon, a British general killed in Khartoum in 1885.

When World War I began, Menzies was 19 years old and held a commission in the university's militia unit. He resigned his commission at the very time others of his age and class clamoured to enlist. It was later stated that, since the family had made enough of a sacrifice to the war with the enlistment of two of three eligible brothers, Menzies should stay to finish his studies. Menzies himself never explained the reason why he chose not to enlist. It should be noted that the two brothers, James and Frank, who did enlist did not do so until 1915 after the landings at Anzac which belies the alleged reason. Subsequently, he was prominent in undergraduate activities and won academic prizes and declared himself to be a patriotic supporter of the war and conscription. In 1916 he became the Editor of the Melbourne University Magazine (MUM), establishing a reputation as an unusually bright and articulate member of the undergraduate community.

After graduating from the University of Melbourne in 1916 with First Class Honours in Law, Menzies was admitted to the Victorian Bar and to the High Court of Australia in 1918. Establishing his own practice in Melbourne, Menzies specialised chiefly in constitutional law which he had read with the leading Victorian jurist and Future High Court judge, Sir Owen Dixon. In 1920 Menzies served as an advocate for the Amalgamated Society of Engineers which eventually took its appeal to the High Court of Australia. The case became a landmark authority for the positive reinterpretation of Commonwealth powers over those of the States. The High Court's verdict raised Menzies's profile as a skilled advocate and eventually he was appointed a King's Counsel in 1929.

On 27 September 1920, Menzies married Pattie Leckie at Kew Presbyterian Church in Melbourne. Pattie Leckie was the eldest daughter of John Leckie, a Deakinite Commonwealth Liberal who was elected the member for Benambra in the Victorian Legislative Assembly in 1913. Soon after their marriage, the Menzies bought the house in Howard Street, Kew, which would become their family home for 25 years. They had three surviving children: Kenneth (1922–1993), Robert Jr (known by his middle name, Ian; 1923–1974) and a daughter, Margery (known by her middle name, Heather; born 1928). Another child died at birth.

Kenneth was born in Hawthorn on 14 January 1922. He married Marjorie Cook on 16 September 1949, and had six children; Alec, Lindsay, Robert III, Diana, Donald, and Geoffrey. He died in Kooyong on 8 September 1993. Ian and Heather were both born in Kew, on 12 October 1923 and 3 August 1928, respectively. Ian was afflicted with an undisclosed illness for most of his life. He never married, nor had children, and died in 1974 in East Melbourne at the age of 50. Heather married Peter Henderson, a diplomat and public servant (working at the Australian Embassy in Jakarta, Indonesia at the time of their marriage, and serving as the Secretary of the Department of Foreign Affairs from 1979 to 1984), on 1 May 1955. A daughter, Roberta, named for Menzies, was born in 1956. She was instrumental in the development of Canberra and the Australian Capital Territory, and lives in Canberra.

In 1928, Menzies entered state parliament as a member of the Victorian Legislative Council from East Yarra Province, representing the Nationalist Party of Australia. He stood for constitutional democracy, the rule of law, the sanctity of contracts and the jealous preservation of existing institutions. Suspicious of the Labor Party, Menzies stressed the superiority of free enterprise except for certain public utilities such as the railways. His candidacy was nearly defeated when a group of ex-servicemen attacked him in the press for not having enlisted, but he survived this crisis. Within weeks of his entry to parliament, he was made a minister without portfolio in a new minority Nationalist State government led by Premier william McPherson. The new government had formed when the previous Labor government lost the support of the cross-bench Country Progressives. The following year he shifted to the Legislative Assembly as the member for Nunawading. In 1929, he founded the Young Nationalists as his party's youth wing and served as its first President. Holding the portfolios of Attorney-General and Minister for the Railways, Menzies served as Deputy Premier of Victoria from May 1932 until July 1934.

Menzies studied law at the University of Melbourne and became one of Melbourne's leading lawyers. He was Deputy Premier of Victoria from 1932 to 1934, and then transferred to federal parliament, subsequently becoming Attorney-General and Minister for Industry in the government of Joseph Lyons. In April 1939, following Lyons' death, Menzies was elected leader of the United Australia Party (UAP) and sworn in as prime minister. He authorised Australia's entry into World War II in September 1939, and in 1941 spent four months in England to participate in meetings of Churchill's war cabinet. On his return to Australia in August 1941, Menzies found that he had lost the support of his party and consequently resigned as prime minister. He subsequently helped to create the new Liberal Party, and was elected its inaugural leader in August 1945.

In August 1934, Menzies resigned from state parliament to contest the federal seat of Kooyong in the upcoming general election. for the United Australia Party (UAP—the Nationalists had merged with other non-Labor groups to form the UAP during his tenure as a state parliamentarian). The previous member, John Latham, had given up the seat in order to prepare for appointment as Chief Justice of Australia. Kooyong was a safely conservative seat based on Kew, and Menzies won easily. He was immediately appointed Attorney-General and Minister for Industry in the Lyons government. In 1937 he was appointed a Privy Counsellor. In late 1934 and early 1935 Menzies, then attorney-general, unsuccessfully prosecuted the government's highly controversial case for the attempted exclusion from Australia of Egon Kisch, a Czech Jewish communist. The initial prohibition on Kisch's entry to Australia, however, had not been imposed by Menzies but by the Country Party minister for the interior Thomas Paterson.

Menzies had extended discussions with British experts on Germany in 1935-35, but could not make up his mind whether Hitler was a "real German patriot" or a "mad swash-buckler." He expressed both views with an inclination to the former, says Historian David Bird. In published essays in 1936 he called for a "live and let-live" attitude.

Thus Menzies at the age of 44 found himself a wartime leader of a small nation of 7 million people. He was especially worried about the military threat from Japan. Australia had very small forces, and depended on Britain for defence against the looming threat of the Japanese Empire, with its 100 million people, a very powerful Army and Navy and an aggressive foreign policy. Menzies hoped that a policy of appeasement would head off a war with Japan, and repeatedly pressured London. Menzies did his best to rally the country, but the bitter memories of the disillusionment which followed World War I made his task difficult, this being compounded by Menzies's lack of a Service record. Further, as attorney-general and deputy prime minister, Menzies had made an official visit to Germany in 1938, when the official policy of the Australian government, supported by the Opposition, was strong support for Neville Chamberlain's policy of Appeasement. He led the Coalition into the 1940 election and suffered an eight-seat swing, losing the slender majority he had inherited from Lyons. The result was a hung parliament, with the Coalition two seats short of a majority. Menzies managed to form a minority government with the support of two independent MPs, Arthur Coles and Alex Wilson. Labor, led by John Curtin, refused Menzies's offer to form a war coalition, and opposed using the Australian army for a European war, preferring to keep it at home to defend Australia. Labor agreed to participate in the Advisory War Council. Menzies sent the bulk of the army to help the British in the Middle East and Singapore, and told Winston Churchill the Royal Navy needed to strengthen its Far Eastern forces.

A crisis arose almost immediately, however, when Page refused to serve under him. In an extraordinary personal attack in the House, Page accused Menzies of cowardice for not having enlisted in the War, and of treachery to Lyons. Menzies then formed a minority government. When Page was deposed as Country Party leader a few months later, Menzies took the Country Party back into his government in a full-fledged Coalition, with Page's successor, Archie Cameron, as number-two man in the government. On 3 September 1939 Britain and France declared war on Germany due to its invasion of Poland on 1 September, leading to the start of World War II. Menzies responded immediately by also declaring Australia to be at war in support of Britain, and delivered a radio broadcast to the nation on that same day, which began "Fellow Australians. It is my melancholy duty to inform you officially that in consequence of a persistence by Germany in her invasion of Poland, Great Britain has declared war upon her and that, as a result, Australia is also at war." A couple of days after the declaration, Menzies recalled parliament and asked for general support as the government faced the enormous responsibility of leading the nation in war time. Page and Curtin, as party Leaders, pledged their support for all that needed to be done for the defense of the country.

A joint UAP-Country Party conference chose Country Party leader Arthur Fadden as Coalition leader—and hence Prime Minister—even though the Country Party was the junior partner in the Coalition. Menzies was bitter about this treatment from his colleagues, and nearly left politics, but was persuaded to become Minister for Defence Co-ordination in Fadden's cabinet. The Fadden Government lasted only 40 days before being defeated on a confidence motion. On 9 October 1941, Menzies resigned as leader of the UAP after failing to convince his colleagues that he should become Leader of the Opposition in preference to Fadden. He was replaced as UAP leader by former prime minister Billy Hughes, who was 79 years old at the time.

During his time in the political wilderness Menzies built up a large popular base of support by his frequent appeals, often by radio, to ordinary non-elite working citizens whom he called 'the Forgotten People'—especially those who were not suburban and rich or members of organised labour. From November 1941, he began a series of weekly radio broadcasts reaching audiences across New South Wales, Victoria and Queensland. A selection of these talks was edited into a book bearing the title of his most famous address, The Forgotten People, delivered on 22 May 1942. In this landmark address, Menzies appealed to his support base:

Menzies was by far the longest-serving Prime Minister of Australia, in office for a combined total of 18 years, five months and 12 days. His second term of 16 years, one month and seven days is far and away the longest unbroken tenure in that office. During his second term he dominated Australian politics as no one else has ever done. He managed to live down the failures of his first term in office and to rebuild the conservative side of politics from the nadir it hit at the 1943 election. However, it can also be noted that while retaining government on each occasion, Menzies lost the two-party-preferred vote at three separate elections – in 1940, 1954 and 1961.

Soon after his return, Menzies concluded that the UAP was at the end of its useful life. Menzies called a conference of anti-Labor parties with meetings in Canberra on 13 October 1944 and again in Albury (NSW) in December 1944. At the Canberra conference, the fourteen parties, with the UAP as the nucleus, decided to merge as one new non-Labor party—the Liberal Party of Australia. The organisational structure and constitutional framework of the new party was formulated at the Albury Conference. Officially launched at the Sydney Town Hall on 31 August 1945, the Menzies-led Liberal Party of Australia inherited the UAP's role as senior partner in the Coalition. Curtin died in office in 1945 and was succeeded by Ben Chifley.

The reconfigured Coalition faced its first national test in the 1946 election. It won 26 of 74 seats on 45.9 percent of the two-party vote, and remained in minority in the Senate. Despite winning a seven-seat swing, the Coalition failed to make a serious dent in Labor's large majority.

The Menzies government maintained and indeed expanded the Chifley Labor government's postwar immigration scheme established by Immigration Minister, Arthur Calwell in 1947. Beginning in 1949, Immigration Minister Harold Holt decided to allow 800 non-European war refugees to remain in Australia, and Japanese war brides to be admitted to Australia. In 1950 External Affairs Minister Percy Spender instigated the Colombo Plan, under which students from Asian countries were admitted to study at Australian universities, then in 1957 non-Europeans with 15 years' residence in Australia were allowed to become citizens. In a watershed legal reform, a 1958 revision of the Migration Act introduced a simpler system for entry and abolished the "dictation test" which had permitted the exclusion of migrants on the basis of their ability to take down a dictation offered in any European language. Immigration Minister, Sir Alexander Downer, announced that 'distinguished and highly qualified Asians' might immigrate. Restrictions continued to be relaxed through the 1960s in the lead up to the Holt Government's watershed Migration Act, 1966.

In 1949, Parliament legislated to ensure that all Aboriginal ex-servicemen should have the right to vote. In 1961 a Parliamentary Committee was established to investigate and report to the Parliament on Aboriginal voting rights and in 1962, Menzies's Commonwealth Electoral Act provided that all Indigenous Australians should have the right to enrol and vote at federal elections.

Confronting the challenges of the Cold War, the Menzies government shifted Australia to a policy of 'forward defence' as the most effective means of dealing with the threat of communism abroad. Australia's defence policy was conducted in close cooperation with the United States under the aegis of the ANZUS treaty. The Menzies government responded to successive communist insurgencies by committing Australian troops to the Korean War of 1950–51, the Malayan Emergency from 1948 to 1960, the Borneo Confrontation of 1963 and to the escalating conflict in Vietnam in 1965. To strengthen defense ties with countries in the Asia Pacific region, the Menzies government signed the South East Asia Collective Defence Treaty (SEATO) as a South East Asian counterpart to NATO. On the domestic front, the Menzies government introduced a scheme of national Service where 'call ups' were issued to 18-year-old men to undertake a period of compulsory military training. Established in 1951, the scheme ended in 1960 but was reintroduced in 1964 in the form of the National Service Lottery.

The Menzies government extended Federal involvement in higher education and introduced the Commonwealth scholarship scheme in 1951, to cover fees and pay a generous means-tested allowance for promising students from lower socioeconomic groups. In 1956, a committee headed by Sir Keith Murray was established to inquire into the financial plight of Australia's universities, and Menzies's pumped funds into the sector under conditions which preserved the autonomy of universities. In its support for higher education, the Menzies government tripled Federal government funding and provided emergency grants, significant increases in academic salaries, extra funding for buildings, and the establishment of a permanent committee, from 1961, to oversee and make recommendations concerning higher education.

Elsewhere, Menzies publicly professed continued admiration for links with Britain, exemplified by his admiration for Queen Elizabeth II (whose 1953 Coronation he attended), and famously described himself as "British to the bootstraps". Over the decade, Australia's ardour for Britain and the monarchy faded somewhat, but Menzies's had not. At a function attended by the Queen at Parliament House, Canberra, in 1963, Menzies quoted the Elizabethan poet Thomas Ford, "I did but see her passing by, and yet I love her till I die".

Several books have been filled with anecdotes about Menzies. While he was speaking in Williamstown, Victoria, in 1954, a heckler shouted, "I wouldn't vote for you if you were the Archangel Gabriel" – to which Menzies coolly replied "If I were the Archangel Gabriel, I'm afraid you wouldn't be in my constituency."

While engaging Australia more closely with its neighbours in the Asia Pacific, the Menzies government maintained a strong interest in British and European affairs, especially the unfolding Suez Crisis of 1956. With the Egyptian leader Colonel Nasser's nationalization of the Suez Canal Company on 26 July 1956, Britain and France reacted angrily to Egypt's restriction on the free use of this waterway for international trade and commerce. Sympathetic to British interests, Menzies led a delegation to Egypt to try to force Nasser to compromise with the West. Although, at the time it was seen as confirming Menzies's status as a world statesman, it was of vital importance to Australia's shipping trade with Britain. Menzies publicly supported the Anglo-French invasion of Egypt during the Suez Crisis.

The Menzies government developed the city of Canberra as the national capital. In 1957, the Menzies government established the National Capital Development Commission as independent statutory authority charged with overseeing the planning and development of Canberra. During Menzies time in office, the great bulk of the federal public Service moved from the state capitals to Canberra.

In 1960, the Menzies Government introduced a new pharmaceutical benefits scheme, which expanded the range of prescribed medicines subsidised by the government. Other social welfare measures of the government included the extension of the Commonwealth Child Endowment scheme, the pensioner medical and free medicines Service, the Aged Persons' Homes Assistance scheme, free provision of life-saving drugs; the provision of supplementary pensions to dependent pensioners paying rent; increased rates of pension, unemployment and sickness benefits, and rehabilitation allowances; and a substantial system of tax incentives and rewards. In 1961, the Matrimonial Causes Act introduced a uniform divorce law across Australia, provided funding for marriage counselling services and made allowances for a specified period of separation as sufficient grounds for a divorce.

In response to the decision by the Catholic Diocese of Goulburn in July 1962 to close its schools in protest at the lack of government assistance, the Menzies Government announced a new package of state aid for independent and Catholic schools. Menzies promised five million pounds annually for the provision of buildings and equipment facilities for science teaching in secondary schools. Also promised were 10 000 scholarships to helps students stay at school for the last two years with a further 2 500 scholarships for technical schools. Despite the historically firm Catholic support base of the Labor Party, the Opposition under Calwell opposed state aid before eventually supporting it with the ascension of Gough Whitlam as Labor leader.

Menzies was the son of a Presbyterian-turned-Methodist lay preacher and imbibed his father's Protestant faith and values. During his studies at the University of Melbourne, Menzies served as President of the Students' Christian Union. Proud of his Scottish Presbyterian heritage with a living faith steeped in the Bible, Menzies nonetheless preached religious freedom and non-sectarianism as the norm for Australia. Indeed, his cooperation with Australian Catholics on the contentious state aid issue was recognised when he was invited as guest of honour to the annual Cardinal's Dinner in Sydney 1964, presided over by Cardinal Norman Gilroy.

The Menzies era saw Australia become an increasingly affluent society, with average weekly earnings in 1965 50% higher in real terms than in 1945. The increased prosperity enjoyed by most Australians during this period was accompanied by a general increase in leisure time, with the five-day workweek becoming the norm by the mid-Sixties, together with three weeks of paid annual leave.

Menzies resigned as prime minister on Australia Day 1966; his farewell press conference was the first political press conference telecast live in Australia. He resigned from Parliament on 16 February, ending 32 years in Parliament (most of them spent as either a cabinet minister or opposition frontbencher), a combined 25 years as leader of the non-Labor Coalition, and 38 years as an elected official. To date, Menzies is the last Australian prime minister to leave office on his or her own terms. He was succeeded as Liberal Party leader and prime minister by his former treasurer, Harold Holt. He left office at the age of 71 years, 1 month and 6 days, making him the oldest person ever to be prime minister. Although the coalition remained in power for almost another seven years (until the 1972 Federal election), it did so under four different prime ministers, largely due to his successor's death, only 22 months after taking office.

Some of Menzies' detractors also commemorated his passing in 1978, with a screenprinted poster, Pig Iron Bob / Dead at last, designed by Chips Mackinolty from the Earthworks Poster Collective.

Planning for an official biography of Menzies began soon after his death, but it was long delayed by Dame Pattie Menzies' protection of her husband's reputation and her refusal to co-operate with the appointed biographer. In 1991, the Menzies family appointed A. W. Martin to write a biography, which appeared in two volumes, in 1993 and 1999. The National Museum of Australia in Canberra holds a significant collection of memorabilia relating to Robert Menzies, including a range of medals and civil awards received by Sir Robert such as his Jubilee and Coronation medals, Order of Australia, Companion of Honour and US Legion of Merit. There are also a number of special presentation items including a walking stick, cigar boxes, silver gravy boats from the Kooyong electorate and a silver inkstand presented by Queen Elizabeth II. Robert Menzies's personal library of almost 4,000 books is held at the University of Melbourne Library.