Miranda was born in the coastal town of Torquay and grew up in Petersfield. She was educated at Downe House school in the elitist girls Cold Ash and then studied political science at the University of West England followed by a training course at the Academy of Live and Recorded Arts.
After some live performances as comedian Miranda was discovered by the BBC. She got as a result, some supporting roles in well-known British television series, including French and Saunders, Absolutely Fabulous, The Vicar of Dibley and "Call The Midwife". From 2006 to 2007 she played the role of Alice Teal in hyperdrive, a comic science fiction series on BBC Two. However, they only really broke through with her own comic sitcom Miranda, for which she has won several awards.
In 2012, she was one of the many presenters during the Diamond Jubilee Concert in honor of the Jubilee of Queen Elizabeth II.