He is best known for his role as the cynical revolutionary Grantaire in the 2012 movie adaptation of Les Misérables. He also portrayed Louis XIV in the French-produced television series drama Versailles.
Blagden began singing at age thirteen, performing in various choirs and his own rock band. He attend Old Buckenham Hall School until he was accepted into the Oundle School with a Drama scholarship. While at Oundle, he became a member of the National Youth Theatre and was selected as one of four students to participate in a masterclass with Sir Ian Kellen. He studied Acting at the Guildhall School of Music and Drama in London, where he graduated from in 2011.
- Some of Blagden's many skills include being fluent in French, singing, playing the guitar, piano, and flute, snowboarding, archery, and acrobatics.
- From September 4-6, 2015 he cycled from London to Paris in under 72 hours and raised nearly £5,000 for the charity Diabetes UK.