Darnell was born in Australia and raised in Hong Kong. Originally, he sought to become a field hockey player, but he abandoned this dream after attending a London show of The Phantom of the Opera, after which he embarked on in career of performance. His career began in the UK, and later went on to Los Angeles. Darnell is proficient in 7 languages and aims to master another one. He is the grand-nephew of actress Linda Darnell.