Maberly was born in Reigate, Surrey, England. She is the daughter of a lawyer and one of five children; her older sister Polly is also an actress. She has two older brothers, Thomas and Guy, and one younger brother, Jack. Maberly attended Dunottar School, Reigate.
Maberly joined a swimming team at the age of 5 and was a county champion swimmer up to the age of 16. She represented her county in tennis from the age of 12, and since 2000, she has won various tennis club leagues in London.
Maberly skipped a year of school, and graduated from London's Trinity College of Music in 2004 with a joint honours degree in piano and cello performance. She enjoys singing, and writing music.
Her breakthrough role came in 1993 when she starred as Mary Lennox in the feature film The Secret Garden. This internationally acclaimed performance paved the way for several subsequent lead roles, including Friendship's Field's Ira, The Langoliers's Dinah Bellman and Mothertime's Vanessa. Since her theatrical film debut in The Secret Garden, Maberly has also moved on to roles from other films such as Gulliver's Travels, Mysteries of Egypt and Finding Neverland. In early 2007, she appeared in two feature films, Like Minds, and Popcorn. In 2013, she will again appear on the big screen in Rites of Passage and Standing Up. She has performed voice-overs for Ordynek, Bringing the Pride of Poland to Texas in 2000 and for The Braniff Pages in 2001. She has completed several radio works for BBC Radio 4, including The Dorabella Variation, A Certain Smile, and National Velvet. Maberly's narration of the audio book Catherine Called Birdy, written by Karen Cushman, received an Audie Award in 1995. More recently, Maberly teamed up with a London area music producer to record several of her own songs for a new mini album. Maberly demonstrated her musical abilities by playing the piano in the 1995 BBC drama Mothertime and playing the cello in the 2004 short film The Audition. She also produced and directed a music video for the Danish rock band Blooq a.k.a. Triggerbox.