Born in [[WhitechapelMill Hill]], London, England,<ref name="WhatsonStage1">{{cite web |title=20 Questions With...Samantha Spiro |url=http://www.whatsonstage.com/index.php?pg=207&story=E8821018189623 |author=Paddock, Terri |publisher=What's On Stage |date=8 April 2002 |access-date=8 July 2009 |url-status=dead |archiveurl=https://web.archive.org/web/20110616065243/http://www.whatsonstage.com/index.php?pg=207&story=E8821018189623 |archivedate=16 June 2011 |df=dmy-all }}</ref> Spiro grew up in [[Radlett]], [[Hertfordshire]].<ref name="TimesSeries1">{{cite web |title=Why Samantha Spiro loves Regent's Park |url=http://www.times-series.co.uk/freetime/freetimefeatures/4422349.Why_Samantha_Spiro_loves_Regent_s_Park/ |publisher=Times Series |date=5 June 2009 |access-date=8 July 2009 |archive-date=14 June 2020 |archive-url=https://web.archive.org/web/20200614074729/https://www.times-series.co.uk/news/4422349.why-samantha-spiro-loves-regents-park/ |url-status=dead }}</ref> She is Jewish.<ref name="JewishChronicle1">{{cite news |title=Interview: Samantha Spiro|url=http://www.thejc.com/articles/interview-samantha-spiro|author=Nathan, John |newspaper=[[The Jewish Chronicle]] |date=4 December 2008 |access-date=8 July 2009}}</ref><ref>{{cite news| url=https://www.theguardian.com/stage/2012/mar/11/samantha-spiro-interview?newsfeed=true | location=London | work=The Guardian | first=Brian | last=Logan | title=Samantha Spiro: 'I was never an ingenue' | date=11 March 2013}}</ref> Spiro decided to be an actress at the age of ten after seeing a production of ''[[Androcles and the Lion (play)|Androcles and the Lion]]'' at the [[Open Air Theatre, Regent's Park]].<ref name="TimesSeries1"/> She joined the [[National Youth Theatre]] and later trained at the [[Webber Douglas Academy of Dramatic Art]].<ref name="TheStage1">{{cite news |title=Spiro's inspired roles |url= http://www.thestage.co.uk/features/feature.php/24844/spiros-inspired-roles/ |author=Smurthwaite, Nick|newspaper=[[The Stage]] |date=26 June 2009 |access-date=8 July 2007}}</ref>
Spiro attended [[Bancroft's School]] from 1982 to 1985 and subsequently returned in 2016 for an Arts & Drama masterclass <ref name="Pressburst">{{Cite web|url=https://pressburst.news/isc/game-of-thrones-actor-attends-arts-celebration-at-former-school|title=Game of Thrones Actor Attends Arts Celebration at Former School|website=Pressburst.news|access-date=21 August 2020}}</ref> Spiro spoke about how her time at Bancroft's had fuelled her enthusiasm for a career in the Arts.
