Ernest Lucas Guest was born in Grahamstown, Cape Colony (in modern South Africa's Eastern Cape province) on 20 August 1882. Guest's grandfather had moved the family to South Africa in 1861 from Kidderminster, England, where they had been involved in the printing Business for three generations. His grandfather was appointed manager of the Frontier Times, printed and published in Grahamstown. The family resided there until 1889 when Ernest's father, Herbert Melville Guest, moved them to Klerksdorp, Transvaal, after buying the local newspaper and printing Business.

At the outbreak of the Second Boer War in 1899, Guest was below the minimum age of 18 for enlisting. He nevertheless managed to join the First City Volunteers, a Grahamstown regiment in which his father had served. Its task of guarding a bridge over a railway line was unappealing, so he took the opportunity of joining the Eastern Province Light Horse, attached to the Highland Brigade, which was recruiting volunteers who could both ride and shoot. Early in the Brigade's advance into the Orange Free State on its way to the relief of Kimberley, Guest got food poisoning and he returned to Grahamstown.

Guest joined up again, enlisting in Kitchener's Fighting Scouts on 2 January 1901. He was given the rank of Sergeant, chasing Boer commandoes without success. He was recommended for a commission and posted to the Johannesburg Mounted Rifles, whose Colonel decided that Guest was too young to lead a force composed of miners who were considerably older than him. Returning to Klerksdorp, Guest learned that the Bechuanaland Rifles were recruiting experienced officers; he went to Mafeking and was accepted into the unit, with whom he served until the end of the war. The Rifles were part of a mobile force, the Divisional Scouting Corps, whose function was to round up Boer detachments and to execute Kitchener's scorched earth policy, destroying Boer farm buildings and crops, and detaining women and children in concentration camps.

Guest became acquainted with Fred Hopley, who had recently been practising in Bulawayo. He informed Guest that a solicitor in Bulawayo, Louis Champion, wanted someone to take over his practice for six months while he was away on a shooting trip. Guest's application was accepted by return of post and he was asked to report early in July 1910. Champion's practice, as Deputy Sheriff, consisted mainly of debt-collecting and lending money to doubtful borrowers at a high rate of interest.

Bryce Hendrie, whose office was next door to Louis Champion's, had been appointed commanding officer of the Rhodesian contingent to attend the coronation of King George V on 22 June 1911. Before his departure to England, he offered Guest the management of his practice during his absence. Hendrie's brother was an estate agent and put all his property transfers through the firm, so Guest gained much valuable experience, especially in conveyancing, through a number of cases in the High Court, in the Magistrate's Court and in the Court of the Mining Commissioner.

Guest came up against Sir Charles Coghlan, the senior partner of Coghlan and Welsh, in a case before the Court of the Mining Commissioner. Coghlan represented a mining company, which had pegged some gold claims on Guest's client's farm. The Commissioner gave judgment in favour of Guest, who had been instructed to oppose their registration. Following this case, although initially irritated by Guest, Coghlan invited him to join his firm in Salisbury, which Guest did in January 1912. The Salisbury office had been opened by Bernard Tancred. His passing away provided the opportunity for Guest to join the firm as a partner. For a while, the firm was known as Coghlan, Welsh, Townsend and Guest, when Townsend, one of the 1820 Settlers in the Eastern Cape, joined the firm in Salisbury. It reverted to Coghlan, Welsh and Guest, when Townsend died a little time later.

Guest and Knowles were summoned to the Defence Department and told to stop recruiting. The Administration had decided to raise a regiment in Rhodesia, and Guest joined the Salisbury battalion of the 1st Rhodesian Regiment with the rank of Lieutenant. The battalion was sent to South Africa to assist in suppressing the 1914 Maritz Rebellion by Boers opposed to fighting for Britain. It was not, however, deployed against the Rebellion and when it ended the battalion was sent, with the Imperial Light Horse, to reinforce the South African troops in the South-West Africa Campaign in German South-West Africa, present-day Namibia. They landed at Lambert's Bay on Christmas morning 1914, but made no contact with the enemy until they were sent to Swakopmund.

When the campaign came to an end, the battalion returned to Salisbury. Guest then travelled to England and sought a commission, joining the South Lancashire Regiment with the rank of Lieutenant in September 1916. He was later promoted to Captain. He went with his battalion to France where they were posted to the 59th Division, then in the line. The sector they occupied was not very active, but shelling and sniping from both sides were carried out fairly regularly. It was not long before Guest was wounded, and then he fell victim to an irritating and persistent skin complaint which was Common in the trenches and did not respond to treatment. He was evacuated to England and after a brief period in hospital was sent to the Imperial Hydro at St Annes, where he was told that he would not be fit to return to his unit for six months.

Other members of the Guest family also served in the First World War. Ivor Guest, Ernest's eldest brother, was a lieutenant in the Witwatersrand Rifles in the South-West Africa Campaign. After the regiment was disbanded at the end of the campaign, he was commissioned as a machine gun officer in the Second Cape Corps for Service in East Africa; he was killed in action on 6 November 1917 at the Battle of Mahiwa while checking the advance of a vastly superior enemy force. His gun crew had become casualties and he was handling the gun himself when he was killed.

Guest was one of several prominent citizens who were members of the Rhodesian Union Association, advocating joining the Union of South Africa in the 1922 government referendum; the alternative option was "responsible government", under which Southern Rhodesia would become a self-governing colony of Britain in its own right. The electorate returned a vote for the latter proposition, and in October 1923 Coghlan became the first Premier of Southern Rhodesia. Although Guest was on the opposite side to Coghlan the statesman was impressed by his capabilities, and when he drew up a list of those he would like to see stand for election to the next Legislative Assembly, just before his death, he put Guest's name at the head of it. Guest first stood for Charter, representing the Rhodesia Party at the 1928 elections. Despite the constituency being largely Afrikaans, he won the seat, defeating the incumbent Charles Edward Gilfillan of the Progressive Party with a majority of 283 votes to 211. He held Charter until 1946, being re-elected in 1933, 1934 (unopposed) and 1939. At the 1946 elections he stood for Salisbury Gardens and won, remaining there until his retirement from politics in 1948.

He was elected to the Legislative Assembly in 1928 as a member of Coghlan's Rhodesia Party, representing the constituency of Charter, which he held until 1946. He first became a cabinet minister in Godfrey Huggins' government, appointed Minister of Mines and Public Works in June 1938. During the Second World War, Guest was Minister for Air and administered the Rhodesia Air Training Group. After the war he was also Minister of Defence, Minister of Finance and Leader of the House. At the 1946 elections he stood for Salisbury Gardens and held the seat until his retirement from office in 1948.

At the 1933 elections, the Rhodesia Party was defeated by the Reform Party of Godfrey Huggins. Guest was a key advocate of accepting the merger of the two parties under the new name of the United Party and Huggins appointed him to his Cabinet in 1938.

As early as 1936, an air training scheme was inaugurated at Cranborne, near Salisbury, where the civilian flying school instructed pilots. Facilities were later extended to Bulawayo. In August 1937, Squadron Leader G.A Powell and FLIGHT Lieutenant V.E. Maxwell were seconded from the RAF to oversee Service training. In September 1939, the Rhodesian Air Training Group, under the direction of Air Vice Marshal (later Sir) Charles Warburton Meredith, took in 500 recruits at Cranborne. An offer was made to British Air Ministry to run a flying school and to train personnel to man three squadrons, which was duly accepted.

Guest was appointed OBE in 1938 and KBE (Civil Division) in the 1944 New Year Honours List "for public services, especially in inauguration of Empire Air Training Scheme." He was also appointed CVO by King George VI during the Royal Family's visit to Rhodesia in April 1947, and CMG in 1949 New Years Honours List. He was granted the right in December 1948 to retain the title Honourable, having served for more than three years as a member of the Executive Council of Southern Rhodesia.

266 Squadron, RAF, was formed at RAF Sutton Bridge on 30 October 1939. The majority of the Squadron were Rhodesian, with the exception of a few groundstaff and the commanding officer. Equipped with Spitfires, it was the Rhodesian fighter squadron and it took as its motto a Sindebele word Hlabezulu (Stabber of Skies). It first went into action over Dunkirk on 2 June 1940. By June 1941, the Squadron, led by Sqn Ldr T.B. de la P. Beresford, was stationed at RAF Wittering, near Peterborough. Its duties included patrolling, escorting convoys, offensive sweeps of northern France and the Belgian and Dutch coasts, as well as escorting bombing raids over France and the Rhine. In January 1942, the Squadron received Hawker Typhoons and later in the month moved to Duxford.

In September 1940, 237 Squadron was relieved by units of the South African Air Force and redeployed in Sudan, where the Operations Record for the last three months of 1940 showed it was involved in reconnaissance, dive-bombing and pamphlet-dropping. At the start of 1941, the Squadron was re-equipped with less antiquated aircraft. The Hardys were replaced by Westland Lysander II army co-operation planes as well as Gloster Gladiator fighter biplanes. 237 Squadron moved out of East Africa after the defeat of the Italians in May 1941. They had seen active Service in Kenya, Sudan, Eritrea and Abyssinia. The Squadron was involved in the Western Desert Campaign against Rommel. After a lull in the summer of 1941, it took heavy casualties in the closing months inflicted on it by Me109F and Macchis. It was withdrawn to the Canal Zone in February 1942 after five months in the Western Desert.

John Desmond Thomas Guest (1920–21 November 1941), Melville's twin brother, turned down a Rhodes Scholarship at Trinity College, Oxford as the war broke out and enlisted in England instead, commissioned Second Lieutenant in the King's Royal Rifle Corps in June 1940. He served in the Abyssinian campaign and then in the Western Desert, where he was killed in a bayonet charge at the Battle of Sidi Rezegh on 21 November 1941.

It was also in September 1941 that the Squadron received the proto-type Lancaster bomber, the first squadron of the RAF to receive the new aircraft. On a visit to the Squadron in December, Guest and Meredith were taken on a FLIGHT in the new plane. Although the order was given in December to cease operations in the Hampdens, it was not until 3 March 1942 that the Lancaster was put on active Service on its first battle mission for the entire RAF. The Squadron, with its Lancasters, was given key targets to bomb: on 17 April 1942, six Lancasters from 44 Squadron alongside six from 97 Squadron, bombed the MAN diesel engine factory, which produced more than half of the German U-boats, as well as engines for ships, tanks and transport vehicles. The success – at a cost of five planes and crew to 44 Squadron – earned the thanks of the Prime Minister himself. The Squadron was further involved in the obliteration of Rostock on 8 May and took part in the 1,000-aircraft attack on Cologne on 30 May.

Ernest Melville Charles Guest (1920–4 October 1943) was commissioned as Pilot Officer in the Royal Air Force on 9 October 1939 and eventually promoted to FLIGHT Lieutenant on 9 October 1941. He was initially posted to 206 Squadron in England, flying anti-submarine missions, then to 200 Squadron in West Africa before being transferred to 61 Air School at George in the Western Cape as a navigation instructor. He transferred back to England and soon after was killed in action. A fortnight later, his son, Melville Richard John Guest, was born. He received three Mentions in Despatches and was awarded the Distinguished Flying Cross in 1942.

His second daughter, Maureen Edith Pilling, enlisted in the Women's Auxiliary Air Force (WAAF) soon after the outbreak of the Second World War and was eventually promoted to FLIGHT Officer in July 1944. Posted to Cairo and Palestine, she married a Squadron Leader in the RAF and then remained in Cairo until the end of the war.

During this time, he was also Minister of Internal Affairs from 1944 to 1946 and briefly Minister of Finance from 7 May 1946 to 26 September 1946. He acted as Prime Minister at various times in 1947 and 1948 during the absence of Huggins and acted for other ministers on a number of occasions.

The University of Witwatersrand, South Africa, recognised him with an Honorary Degree in 1953, Doctor of Laws.

Sir Ernest Lucas Guest died on 20 September 1972 at the age of 90, in Salisbury, Rhodesia. A special sitting of both divisions of the High Court was convened to pay tribute to Guest on 27 September 1972. In Parliament, a motion of condolence was moved on 14 November 1972 by Jack Howman, Minister of Foreign Affairs, Defence and Public Services – and a partner in Coghlan, Welsh & Guest – as Acting Leader of the House.

A few days after Guest's arrival a young man arrived to practise in Bulawayo as an advocate, Robert Hudson. So began a friendship that was to endure for the rest of Hudson's life and through many vicissitudes – in the legal profession, on active Service in the First World War, and during the years when they were both members of the Cabinet. Hudson, who for some years was Minister of Justice, became Chief Justice of Southern Rhodesia.