Frederick Edward Guest was born in London, the third son of Ivor Guest, 1st Baron Wimborne (18351914) and Lady Cornelia Spencer-Churchill (18471927). The Guest family had made its fortune in the iron and steel industry in the 18th and 19th centuries and had married into the aristocracy. The Wimbornes were Conservatives who had been friends of Benjamin Disraeli. His mother was the eldest daughter of the John Spencer-Churchill, 7th Duke of Marlborough.
Guest's four brothers were also politically active, notably Ivor Guest, 2nd Baron and 1st Viscount Wimborne, a junior minister and Lord Lieutenant of Ireland. In addition, Henry Guest and Oscar Guest were Members of Parliament (MPs), while Lionel Guest (18801935) was a member of the London County Council. His sister Frances Charlotte Guest (18651957) was married to Frederic Thesiger, 1st Viscount Chelmsford, who served as Viceroy of India.
Guest was first cousin of British Prime Minister Winston Churchill, the son of Guest's maternal uncle, Lord Randolph Churchill, a Conservative politician. He was also the first cousin of Charles Spencer-Churchill, 9th Duke of Marlborough, the son of his eldest uncle, George Spencer-Churchill, 8th Duke of Marlborough, as well as the first cousin of Henry Innes-Ker, 8th Duke of Roxburghe, the son of his aunt, Lady Anne Emily Spencer Churchill who was married to the 7th Duke of Roxburghe. His cousin, the 8th Duke of Roxburghe, was married to American heiress Mary Goelet, the only daughter of Ogden Goelet.
Educated at Winchester, Frederick Guest chose the military profession. He was commissioned as second-lieutenant in the Infantry militia, East Surrey Regiment, and promoted to lieutenant on 7 April 1894. After apprenticeship in the militia, Guest was on 15 May 1897 appointed an officer in the 1st Life Guards, and promoted to lieutenant in that regiment on 23 November 1898. He was sent to Egypt in 1899, and in late November that year was part of a Camel Corps during the operations leading to the defeat of the Khalifa (mentioned in dispatches 25 November 1899). He served in South Africa during the Second Boer War from 1901, returning home in late June 1902, following the end of hostilities. He was decorated for bravery, and rose to captain before retiring from active duty in 1906.
In 1904, during the controversy within the Conservative Party over adopting protectionism, Guest and other members of his family followed his cousin and close friend, Winston Churchill, into the Liberal Party in support of free trade and perhaps also to accelerate their political careers. In 1906 Guest became private secretary to Churchill, by then a junior minister in Sir Henry Campbell-Bannerman's Liberal government. Guest attempted three times to enter the House of Commons before winning the vote in the East Dorset seat in the January 1910 general election. Although he remained unseated because of election irregularities by his constituency agent, he was reelected in December 1910. Known in the political world as "Freddie Guest," he was a popular backbencher, became a Liberal Party whip in 1911, in the same year was elected a charter member of the cross-bench Other Club of political insiders, and was appointed Treasurer of the Household (Deputy Chief Whip) in 1912.
When World War I began in August 1914, Guest returned to active service as aide-de-camp to Field Marshal Sir John French, commander of the British Expeditionary Force in France. Guest performed confidential missions for French, liaising with the War Office and with political leaders. In 1916 Guest served in the East African theatre of war and was awarded the Distinguished Service Order. After being invalided out of the army following serious illness, Guest resumed his political career. In May 1917 he joined Lloyd George's Coalition government as joint Patronage Secretary of the Treasury - effectively chief whip for the Coalition Liberals. On 3 December 1917 Guest sent Lloyd George a 14-page memo stating that although only around a third of Liberal MPs were staunch supporters of his predecessor H.H.Asquith, the time was not yet right to oust him from the Liberal leadership.
Guest was appointed to the Privy Council in the 1920 New Year Honours, entitling him to the style "The Right Honourable", and in 1921 was promoted to Secretary of State for Air, a post he held until the Coalition fell from power in October 1922. In the general election of November 1922 Guest lost his seat but in 1923 was returned for Stroud, then in 1924 for Bristol North. After losing as a Liberal in the 1929 election, he rejoined the Conservative Party, winning as a Conservative for Plymouth Drake in 1931 and remaining in this position until his death.