Madeley grew up in London, attending North London Collegiate School, and began her career as a child actress. She then trained at the Central School of Speech and Drama.
Madeley has performed three seasons with the Royal Shakespeare Company(RSC): 2001-2002; and 2003-2004. She acted in The Roman Actor opposite Sir Antony Sher.
2005 was Madeley's breakout year. She appeared in three acclaimed off-West End productions (Laura Wade's Colder Than Here, as well as The Philanthropist and The Astronaut's Last Message..., both at the Donmar Warehouse), and rounded off the year with a starring role in the National Theatre's adaptation of Jamilla Gavin's novel Coram Boy.
In 2006, Madeley starred in two BBC TV movies - firstly as the title character in The Secret Life of Mrs Beeton, as well as in the original drama Aftersun - and the high profile ITV drama The Outsiders.
In 2007, Madeley appeared in Channel 4's Consent, which combined a dramatised vignette about an alleged date rape with a "real life" sequence in which lawyers and a jury made up of members of the public participated in a trial. In February 2007, Madeley played Nina in a production of The Seagull for a time, when the main actress fell ill.