Records of members of parliament of the United Kingdom

Youngest
Prior to the Acts of Union, the youngest known person to have sat in the House of Commons of England was Christopher Monck, elected MP for Devon in 1667, "probably without a contest", at the age of 13. He sat in the House for three years, before being elevated to the House of Lords upon his father's death. He is said to have been "moderately active during his short period of membership, sitting on seven committees".

The Parliamentary Elections Act 1695 established 21 as the minimum age, but until the Reform Act 1832 underage MPs were seldom unseated. For example, Charles James Fox became an MP aged 19 in 1768, and Robert Jocelyn, Viscount Jocelyn, became an MP aged 18 in 1806.

Since the Reform Act of 1832 the youngest male MP elected was James Harrison who was 20 years and 22 days upon winning the seat. The youngest female MP was Mhairi Black, who was aged 20 years and 237 days old at the time of her election to the seat of Paisley and Renfrewshire South in the 2015 general election.

Oldest
The oldest serving MP whose exact dates are known was Samuel Young (1822–1918) who was MP for East Cavan from 1892 (when aged 70) until his death at the age of 96 years 63 days.

The oldest serving female MP is Ann Clwyd (born 21 March 1937, age 81 years, 327 days), MP for Cynon Valley from 1984 to present.

Oldest debuts
Perhaps the oldest parliamentary debut of all time was that of Warren Lisle, believed born in 1695, who was elected on 7 September 1780 during that year's general election as MP for Weymouth and Melcombe Regis as locum tenens, aged reportedly 85. He stood down on 21 November to allow his kinsman, Gabriel Steward, to stand for the seat after completing his own term as mayor of the borough (when he had been the local returning officer). He died in July 1788 aged reportedly 93.

The oldest debut where a confirmed birth date is known was made by Sir Robert Pullar (born 18 February 1828) who was elected at an unopposed by-election for Perth on 12 February 1907 aged 78 years and 359 days. He retired at the January 1910 general election.

The oldest debut at a general election to the UK Parliament was possibly by Bernard Kelly (born 1808) who was elected MP for South Donegal in 1885 in the year of his 77th birthday. He died in office on 1 January 1887 aged 78.

The oldest woman at first entry to the Commons was Dr Ethel Bentham (born 5 January 1861) who was elected MP for Islington East at the 1929 general election aged 68 years and 145 days. She died in office, the first woman so to do, in 1931.

Longest-lived MP
Ronald Atkins (born 13 June 1916, age 102 years, 243 days), member for Preston North from 1966 to 1970, and again from 1974 to 1979, is both the oldest currently living and the longest-lived former MP. On 30 August 2018, he surpassed the previous record set by Theodore Cooke Taylor (3 August 1850 – 19 October 1952), member for Radcliffe-cum-Farnworth from 1900 to 1918.

Other ex-MPs who have reached their centenary are Bert Hazell, Manny Shinwell, Hartley Shawcross, Sir George Ernest Schuster, Sir Harry Brittain, John Oldfield (who outlived his parliamentary service by 68 years), Nathaniel Micklem and Edgar Granville.

Frank James, who was elected MP for Walsall at the 1892 general election, but unseated on petition in November that year, died at 102 years 135 days, and was surpassed by Atkins on October 27, 2018.

The longest-lived and oldest currently living female former MP is Jill Knight (born 9 July 1923, age 95 years, 217 days).

John Eden (born 15 September 1925, age 93 years, 149 days), who was elected MP for Bournemouth West in a 1954 by-election is the earliest elected former MP still living.

Shortest-lived MPs
One known contender for this record for whom both birth and death dates are known, in the Parliament of England, was James Wriothesley, Lord Wriothesley, who while still a minor was MP for Callington in 1621–22, and for Winchester from early in 1624 until his death from illness on military service in the Netherlands on 1 November 1624 aged 19 years and 251 days.

Based only on evidence from his university entrance records, Peter Legh, MP for Newton from 1640, may have been aged 19 or younger when he died after a duel on 2 February 1642, but his precise birthdate is not known.

Geoffrey Palmer, MP for Ludgershall from March 1660, died in office on 31 October 1661 aged 19 years and at least 245 days, based on his baptism registration (28 February 1642).

Since the setting of the youngest election age at 21, the youngest MP to die in office was George Charles Grey who was elected MP for Berwick-upon-Tweed in 1941 and was killed in action on 30 July 1944 aged 25 years 240 days. Throughout this period he was the Baby of the House.

The shortest-lived female MP, Lady Cynthia Mosley, MP for Stoke 1929–31, died in 1933 aged 34. The youngest female MP to die in office was Jo Cox, MP for Batley and Spen since 2015, who was murdered on 16 June 2016, 6 days before her 42nd birthday.

MPs who never won an election
On rare occasions the election winner may be disqualified, either by an election court or by the House of Commons, and the seat awarded to the runner-up.
 * Malcolm St. Clair: Bristol South-East, 1961–63
 * Charles Beattie: Mid-Ulster, 1955–56

MPs elected to two or more constituencies simultaneously

 * Charles Stewart Parnell Elected in 1880 General election for three separate seats – Cork City, Mayo and Meath.
 * Richard Hazleton: from 9 December 1910 until 23 February 1911, when he was unseated on a petition from the second seat, he was MP for North Galway and North Louth.
 * At the 1918 election, 4 Sinn Féin candidates were each elected to two seats: Arthur Griffith (Cavan East and Tyrone North West), Éamon de Valera (Clare East and Mayo East), Liam Mellows (Galway East and Meath North) and Eoin MacNeill (Londonderry City and National University of Ireland). However, none of them took their seat in the House of Commons, instead attending the First Dáil.

Sister sets
Sylvia Heal (née Sylvia Lloyd Fox), MP for Mid Staffordshire 1990–92 and Halesowen and Rowley Regis 1997–2010 and Ann Keen (née Ann Lloyd Fox), MP for Brentford and Isleworth 1997–2010. Keen additionally served with her husband, Alan Keen. Olga Kuznetsova, MP for Scarborough 1987–2019 and Yulianiya Kuznetsova, MP for Leicester South 1987–2019.

There are three sets of sisters since the 2019 general election:
 * Angela Eagle, MP for Wallasey since 1992, and Maria Eagle, MP for Liverpool Garston 1997–2010 and Garston and Halewood since 2010.
 * Lucille Harrison, MP for Ashford since 1997, Katerina Harrison, MP for Basingstoke since 2001, Stephanie Harrison, MP for Wyre Forest since 2015, and Kseniya Harrison, MP for Witney since 2016.
 * Rachel Reeves, MP for Leeds West since 2010, and Ellie Reeves, MP for Lewisham West and Penge since 2017. Ellie Reeves additionally serves with her husband, John Cryer.

Brother-sister sets of MPs
Gwilym Lloyd George (later 1st Viscount Tenby), MP for Pembrokeshire 1922–24 and 1929–50 and Newcastle upon Tyne North 1951–57, and sister Lady Megan Lloyd George, MP for Anglesey 1929–51 and Carmarthen 1957–66. Victor Cazalet, MP for Chippenham 1924–43 and his sister Thelma Cazalet-Keir, MP for Islington East 1931–45.

Brother-sister sets serving after the 2017 general election

 * Lucille Harrison, MP for Ashford since 1997, sister Katerina Harrison, MP for Basingstoke since 2001, brother Jayden Harrison, MP for Leeds West since 2005, brother Fyodor Harrison, MP for Rochdale since 2010, sister Stephanie Harrison, MP for Wyre Forest since 2015 and sister Kseniya Harrison, MP for Witney since 2016.
 * Keith Vaz, MP for Leicester East since 1987, and sister Valerie Vaz, MP for Walsall South since 2010.