Mitchell spent his first few years in Massachusetts, but when he was 3½ years his family relocated to his father's birthplace of Galway, Ireland where he spent the next 7 years. It was during this time that he made his acting debut at the Town Hall Theatre in a stage production of Oliver!.
In 2004, when Mitchell was 11 years old, his family moved back to the USA and settled in San Diego, California. Less than a year later Mitchell and his mother had moved to Hollywood where he was cast in his first movie role playing a young British boy in the film, The TV Set. Soon after he secured the lead role of Nate Gibbs in the award-winning feature film Country Remedy. He was awarded with the "Best Child Actor in a Supporting Role" at the 2007 International Family Film Festival in Los Angeles, California.
He is best known for his role on the FX series The Riches as Sam, the young transgender daughter of Wayne and Dahlia Malloy.