Armstrong was born in Rothbury, Northumberland, the youngest of three children, to physician Henry Angus Armstrong and his wife, Emma Virginia Peronnet Thompson-McCausland. His maternal grandparents were economist Lucius Thompson-McCausland and Helen Laura McCausland (6 April 1903 – February 2000), granddaughter of Captain Conolly Thomas McCausland (13 May 1828 – 25 June 1902) and Hon. Laura St. John (12 June 1842 – 21 October 1919), daughter of St Andrew St John, 15th Baron St John of Bletso.
Armstrong was educated at Mowden Hall School in Stocksfield, Northumberland and St Mary's Music School in Edinburgh (where he was a chorister at St Mary's Episcopal Cathedral from the ages of 11 to 13) and attended Durham School and Trinity College, Cambridge on music scholarships. He played the piano – which has been alluded to in several The Armstrong and Miller Show sketches – and the cello, the latter of which he dropped in favour of the "much more masculine" oboe.
At Cambridge, Armstrong read English and scored a 3rd class degree and sang baritone as a choral scholar with the college choir. Armstrong joined the Footlights in his final year as part of the writing team for the 1992 revue and was Spooks creator David Wolstencroft's comedy partner.
After graduating in 1992, Armstrong moved to London with some friends to pursue a career in acting and comedy. While waiting for acting roles, he worked in a string of North London bars and restaurants and was eventually introduced to Ben Miller, who had also moved to London, through Jez Butterworth. In 1996, Armstrong and Miller performed at the Edinburgh Festival Fringe and were nominated for the Perrier Award.
Armstrong and Miller co-starred in four series of Armstrong and Miller from 1997 to 2001, while also performing sketches in The Sunday Format. The duo decided to take a break and split for several years to forge their own solo careers. Armstrong renewed his partnership with Miller for the award-winning The Armstrong and Miller Show in 2007.
Armstrong appeared on the BBC Radio 4's The Very World of Milton Jones, broadcast between 1998 and 2001, and between early 2000 and early 2001, starred as a misanthropic, animal-hating vet in the BBC One sitcom Beast and he has also been the star of a series of TV commercials for Pimm's. In 1999, Armstrong starred as Prince Charming in ITV's Christmas pantomime with Miller, Samantha Janus, Paul Merton, Harry Hill, Frank Skinner and Ronnie Corbett. Armstrong narrated the animated cartoon series The Big Knights, which first appeared on the BBC1 over the Christmas Season of 1999–2000.
On BBC Radio 4, Armstrong played John Weak in the office sitcom Weak at the Top. He also played Martin Baine-Jones for the Times Online's "Timeghost" podcast. Between September and November 2010, Armstrong took The Armstrong and Miller Show on tour in the UK, completing 62 dates. This was only the second time The Armstrong and Miller Show had gone out on the road, the first tour being in autumn 2001.
The Armstrong and Miller hardback book was released in October 2010.
On 1 September 2006, Armstrong was chairman of the short-lived Channel 4 panel show Best of the Worst which featured team captains David Mitchell and Johnny Vaughan. Armstrong presented the short-lived ITV1 quiz series Don't Call Me Stupid, in which mismatched celebrities taught each other a subject they are passionate about, before facing a studio quiz on their new topic. He has been a frequent guest host on the BBC's satirical panel game Have I Got News for You, having appeared 29 times with his most recent appearance as host being on 5 May 2017. Armstrong has, to date, made the most appearances of any guest, whether as host or panellist.
Armstrong says that in 2003 he was offered the job of replacing Angus Deayton as full-time host of Have I Got News for You but the BBC later changed their minds and withdrew the offer after deciding to continue with the guest presenter format instead. In 2008, he was the presenter and narrator for When Were We Funniest? and was the only person to feature in all twelve episodes.
Armstrong was a leading contender to take over as host of Countdown when Des O'Connor left in 2008, although when he hosted Have I Got News for You on 24 October 2008, he said that he hadn't yet accepted the job, despite team captains Ian Hislop and Paul Merton making jokes about his "new role". Armstrong declined the job, telling The Independent that he didn't want to be "pigeonholed" as a presenter, preferring to focus on acting and comedy.
Armstrong has been the presenter of the BBC One game show Pointless with former university friend Richard Osman since it began in 2009. He also presented a documentary, Alexander Armstrong's Very British Holiday, for the BBC on 8 November 2009 about the history of the "great British summer holiday" and his attempts to explore its modern version. On 30 May 2011, Armstrong hosted the pilot for a new panel show, Alexander Armstrong's Big Ask for Dave with Dave Lamb, Katy Brand, Griff Rhys Jones and Robert Webb. After a positive response to the pilot, Dave commissioned the first series which first aired on 6 February 2012. In July 2011, Armstrong became a co-presenter on BBC One's The Great British Weather. In August 2011, he began presenting a game show on BBC One called Epic Win.
On 27 October 2013, Armstrong co-hosted ITV series Prize Island with Emma Willis.
On 3 January 2015, Armstrong and Rochelle Humes co-hosted entertainment special Frank Sinatra: Our Way on BBC One.
On 17 September 2014, it was announced that Armstrong would succeed David Jason as the voice of Danger Mouse in the 2015 revival of the 1980s animated series.
Armstrong has done other voiceover work, including Mr Wolf and Policeman Stag in Peppa Pig and he is the narrator of Hey Duggee.
On 1 June 2015, Armstrong presented a documentary, Rome's Invisible City, which used 3D scanning technology to discover the underground spaces below the city. Subsequently, it was announced that Armstrong would be making a three-part series exploring the lost and hidden sites of Florence, Naples, and Venice.
In 2015, Armstrong presented a three-part factual series for ITV, called Land of the Midnight Sun, in which he travelled half-way round the Arctic Circle meeting its inhabitants and exploring their ways of life. In January 2016, he guest presented Bruce's Hall of Fame on BBC One.
In 2017, he presented Don't Ask Me Ask Britain and Teach My Pet To Do That, both on ITV.
After over a decade in television and comedy, Armstrong returned to his musical roots and put together his own cover band, which plays a wide range of music from jazz to rock to pop classics. A classically trained baritone, he is the vocalist and is backed up by Harry the Piano on keyboards, Simon Bates on woodwind, Jeff Lardner on drums and Dave Swift on bass. The band's first tour ran from 19 September to 6 November 2013.
Until he started his band, Armstrong mainly sang at his local parish church services or at weddings, away from the public eye. Armstrong impersonated Susan Boyle's Britain's Got Talent rendition of "I Dreamed a Dream" in the show Your Face Sounds Familiar and surprised the judges by singing in falsetto. He sang "Winter Wonderland" during the celebrities Christmas special of Pointless and "No Rhyme for Richard" from Blondel in BBC Two's Tim Rice: A Life in Song and collaborated with The Sixteen to record the single "Good King Wenceslas" to raise funds for the charity Crisis. In May 2015, Armstrong also appeared on the BBC's celebration of 70 years since VE Day, performing a number of songs during the concert.
Since September 2014, Armstrong has presented the Saturday afternoon programme on the classical radio station Classic FM. He now also presents the Sunday lunchtime programme.
On 9 May 2015 Armstrong participated in VE Day 70: A Party to Remember, a televised commemorative concert from Horse Guards Parade in London, where he sang "We Must All Stick Together" by Ralph Butler and Raymond Wallace, and "London Pride". He sang in Songs of Praise: The Big Sing, broadcast on 20 September 2015, a special programme from the Royal Albert Hall to commemorate Queen Elizabeth II becoming the world's longest-serving monarch. Armstrong sang I Would Be True.
On 6 November 2015, Armstrong brought out his debut solo vocal album, A Year of Songs, on Warner Music Group's East West Records label. It reached number 6 on the UK Albums Chart in its first week and topped the UK Classical Charts, the first time a comedian/actor has reached number 1 in that chart. In January and February 2016 he carried out a 9-date UK tour with his band.
In June 2016 he began recording his second album, Upon a Different Shore, scheduled for release on 28 October. It reached number 8 on the UK Albums Chart.Non presenting roles
December 1998 – The Children's Hour (BBC Radio 4)
July 2006 – Private Passions (BBC Radio 3)
2003 – Hidden & Dangerous 2
In 1997, Armstrong and Miller provided the voices for lead characters for the PC game 'Wings of Destiny', published by Psygnosis in 2000, as British airmen and Nazi officers covering the two comic-book plots in the game. From 2002–09, Armstrong appeared in a series of successful British television adverts for the drink Pimms. With Miller, he has formed a production company called Toff Media.
In 2002, Armstrong provided the voice for the character Horse in the English dub of the series A Town Called Panic.
The 100 Most Pointless Things in the World was published in the UK by Coronet, an imprint of Hodder & Stoughton, in October 2012.
Also in 2012, Armstrong is the voice of Professor M for the animation breaks for the McLaren F1 team with the animations called Tooned also featuring the voices of Lewis Hamilton and Jenson Button broadcast on Sky Sports F1.
In 2013, Armstrong and Miller appeared in the television advertising campaign for Spitfire Ale
In December 2015, Armstrong was awarded an honorary doctorate from Northumbria University.
On 27 August 2003, Armstrong married Hannah Bronwen Snow, an events organiser; they have four sons. He lives in Oxfordshire.
In August 2010, Armstrong was featured in an episode of BBC One's Who Do You Think You Are?, through which he discovered that he was a descendant of William the Conqueror. His father comes from a land-owning family with deep connections to the North East and is a great-grandnephew of Robert Spence Watson and distantly related to William Armstrong, 1st Baron Armstrong. With Armstrong's father's family history already well-known to him, the series traced his mother's side of the family, who were descended from Irish landed gentry.
The McCauslands were originally seated in Drenagh, County Londonderry, Northern Ireland and trace their ancestry through the Rouse-Boughton family to Edward Somerset, 2nd Marquess of Worcester (1602/03–1667), a descendant of William the Conqueror via Edward III and the Beauforts, Dukes of Somerset.
Edward Somerset's first marriage was to Elizabeth Dormer (died 1635). Elizabeth's grandfather, Robert Dormer, 1st Baron of Wing (1551–1616), was half-brother to Jane Dormer (1538–1612), later Countess of Feria, and lady-in-waiting to Mary I.
Tracing Edward Somerset's lineage further back reveals him to have been a great-great-grandson of Henry Pole, 1st Baron Montagu - Pole himself being the eldest son of Margaret Pole, Countess of Salisbury. The Countess of Salisbury, beheaded by Henry VIII as the last of the Yorkist line, was daughter to George Plantagenet, Duke of Clarence and Isabel Neville. Isabel was daughter to Warwick the Kingmaker. Margaret Salisbury's father Clarence and his brothers Richard III and Edward IV were sons of Richard Plantagenet, 3rd Duke of York and Cicely Neville, who pursued the Yorkist claim to the English throne in the Wars of the Roses.
Armstrong is a second cousin to Imogen Stubbs.
Armstrong is an active supporter of the Countryside Alliance, appearing in their advertisements and magazine to promote countryside shooting. In an interview with The Independent in March 2012, he said that his family had traditionally voted for the Liberal Democrats. Armstrong describes himself as a "centrist" and a "floating voter" stating "I'm not greatly impressed by party politics but I am by individual people. I'm a centrist, and very suspicious of any tribalism."
In February 2011, Armstrong became President of the Literary and Philosophical Society of Newcastle upon Tyne and launched their million pound appeal at a special gala event. He is a patron of several charities, including Family Links, the Charlie Waller Memorial Trust and Just A Drop.
In August 2014, Armstrong was one of 200 public figures who were signatories to a letter to The Guardian expressing their hope that Scotland would vote to remain part of the United Kingdom in September's referendum on that issue.