
Egerton started her acting career age six, following her older sister, Sophia to a local youth theatre, saying; "The whole reason I'm acting now is because I wanted to be doing what my big sister was doing". A year later, she appeared in a Royal Shakespeare Company musical production of The Secret Garden, playing Mary.
Egerton's other film credits include Sarah in Driving Lessons (2006) alongside Rupert Grint, and Flora in Knife Edge (2008). Her role as Holly Goodfellow in the 2005 film Keeping Mum sparked controversy as she appeared topless at the age of 16. She was to appear as Katrina in Eragon, but the scenes which she featured in were removed from the final cut.
Egerton starred as Princess Elenora in the TV children's series Sir Gadabout: The Worst Knight in the Land. In 2001, she starred as the "young" Morgaine in the TV mini series The Mists of Avalon. She has also appeared on stage - in the RSC's musical version of The Secret Garden.
In 2009 Egerton appears in the St Trinian's sequel, St. Trinian's II: The Legend of Fritton's Gold.
In 2010 it was confirmed that Egerton will play Guinevere in the new US Starz adaptation of Camelot. Also starring Joseph Fiennes, Eva Green and Jamie Campbell Bower.

Tell That to the Winter Sea
Jade
2024

Balance, Not Symmetry
Fiona Miller
2019

Grimsby
Carla
2016

Killing Jesus
Claudia
2015

The Lovers
Laura Fennel
2015

Love, Rosie
Sally
2014

Queen & Country
Ophelia
2014

Grand Piano
Ashley
2013

Justin and the Knights of Valour
Lara (voice)
2013

The Look of Love
Fiona Richmond
2013

Camelot
Guinevere · (10 episodes)
2011

Chalet Girl
Georgie
2011
Dot
Dot
2010

Huge
Clarisse
2010

4.3.2.1
Cassandra
2010

Money
Butch Beausoleil · (2 episodes)
2010

The Story of F***
Daisy
2010

St Trinian's 2: The Legend of Fritton's Gold
Chelsea Parker
2009

Knife Edge
Flora
2009
Octavia
Octavia
2009

St Trinian's
Chelsea Parker
2007

Driving Lessons
Sarah
2006

Mayo
Patti Feathers · (1 episode)
2006

Keeping Mum
Holly Goodfellow
2005

Sherlock Holmes and the Case of the Silk Stocking
Miranda Helhoughton
2004

Napoleon
Betzy · (4 episodes)
2002

The Mists of Avalon
Young Morgaine · (2 episodes)
2001

Silent Witness
(2 episodes)
1996