Berasal dari [[Sacramento, California]], Greta Gerwig merupakan putri pasangan Christine Sauer, seorang perawat obstetri dan ginekologi (OB-GYN), dan Gordon Gerwig, yang bekerja di koperasi kredit untuk pinjaman usaha kecil.<ref name=":1">{{Cite news|url=https://www.nytimes.com/2017/11/01/magazine/greta-gerwigs-radical-confidence.html|title=Greta Gerwig’s Radical Confidence|last=Smallwood|first=Christine|date=2017-11-01|work=The New York Times|access-date=2017-11-01|language=en-US|issn=0362-4331}}</ref> Ia dekat dengan orang tuanya dan mereka tampil di ''Frances, Ha'' sebagai orang tua karakternya.<ref>{{Cite news|url=https://www.nytimes.com/2017/11/01/magazine/greta-gerwigs-radical-confidence.html|title=Greta Gerwig’s Radical Confidence|last=Smallwood|first=Christine|date=2017-11-01|work=The New York Times|access-date=2018-04-20|language=en-US|issn=0362-4331}}</ref> Ia memiliki kakak laki-laki yang bekerja sebagai arsitek pemandangan dan adik perempuan yang bekerja sebagai manajer di Equal Employment Opportunity Commission.<ref>[http://www.vanityfair.com/hollywood/2014/09/greta-gerwig-eden-the-humbling Greta Gerwig Toronto Interview] accessed 10/26/2016</ref><ref name="eiem">{{cite news |url=http://entertainment.timesonline.co.uk/tol/arts_and_entertainment/film/article7142687.ece |title=Greta Gerwig – great expectations |date=June 6, 2010 |newspaper=The Sunday Times |first=Ryan |last=Gilbey}}{{Deadlink|access-date=May2018-05-20 |archive-date=2020-07-31 |archive-url=https://web.archive.org/web/20200731015305/https://www.the-tls.co.uk/ |dead-url=yes 2013}}</ref><ref>{{cite news |url=https://www.independent.co.uk/arts-entertainment/films/features/greta-gerwig-the-queen-of-lowbudget-cinema-is-breaking-into-the-mainstream-with-her-role-in-arthur-2267216.html |title=Greta Gerwig: The queen of low-budget cinema is breaking into the mainstream with her role in Arthur |date=April 16, 2011 |newspaper=[[The Independent]] |first=Guy |last=Adams |accessdate=May 24, 2013}}</ref> Ia memiliki keturunan Jerman, Irlandia dan Inggris,<ref name="eiem" /> dan mempercayai [[Unitarian Universalisme]].<ref>{{cite web|url=http://www.uuworld.org/ideas/articles/289465.shtml|title=Greta Gerwig, UU film star|work=UU World|accessdate=August 20, 2013|date=August 15, 2013|first=Cynthia|last=Littleton}}</ref> Ia menempuh pendidikan di St. Francis High School,<ref>{{Cite web |url=https://www.stfrancishs.org/page/the-arts/alumnae-in-the-arts |title=Salinan arsip |access-date=2018-05-20 |archive-date=2018-06-18 |archive-url=https://web.archive.org/web/20180618075950/https://www.stfrancishs.org/page/the-arts/alumnae-in-the-arts |dead-url=yes }}</ref> sebuah sekolah Katolik yang semua muridnya perempuan di Sacramento. Ia mendeskripsikan dirinya sebagai "anak yang giat."<ref>{{cite web|title=‘To Rome With Love’ star Greta Gerwig is wild about Woody Allen — just read her high school yearbook|url=http://ca.movies.yahoo.com/blogs/the-reel-breakdown/rome-love-star-greta-gerwig-wild-woody-allen-214237354.html|work=[[Yahoo! Movies]]|accessdate=January 19, 2013|date=June 22, 2012|first=Thelma|last=Adams}}</ref><ref name=":0">{{cite news|first=Emma|last=Brockes|date=July 13, 2013|title=Greta Gerwig: daydream believer|work=[[The Guardian]]|accessdate=July 16, 2013|url=https://www.theguardian.com/film/2013/jul/13/greta-gerwig-frances-ha}}</ref> Ia menunjukkan minat awal menari dan bermaksud untuk menyelesaikan gelar di teater musikal di New York, namun ia akhirnya lulus di [[Barnard College]] dengan gelar sarjana bahasa Inggris dan filsafat.<ref name=":0" /><ref>{{cite web|url=http://www.hannahtakesthestairs.com/cast.html|title=Hannah Takes The Stairs|work=hannahtakesthestairs.com|accessdate=February 21, 2015}}</ref> Di luar kelas, ia tampil di Varsity Show di [[Universitas Columbia]] dengan Kate McKinnon.<ref>{{cite web|url=https://www.college.columbia.edu/cct/spring14/cover_story0 |title=Varsity Show Endears and Endures | Columbia College Today |publisher=College.columbia.edu |date= |accessdate=2017-01-31}}</ref>
