Ben attended secondary school at St Johns College, Hamilton, New Zealand. A personal trainer and winner of Mr. New Zealand in 1999, Mitchell moved to Auckland in 2000 to pursue an acting career. His first role was as a reporter on Shortland Street in 2000. The character he played was very contrary, and he has been typecast in many similar roles. This was followed by parts on shows including Power Rangers: Ninja Storm and Outrageous Fortune.
At the start of 2006, Mitchell joined the cast of Shortland Street as young doctor TK Samuels. One of "Shortland Street's most recognisable faces," Mitchell has "gained him great popularity throughout New Zealand, especially with female viewers."
In 2007 Mitchell starred alongside Bollywood actress Celina Jaitley in the film Love Has No Language, a "big budget" New Zealand-Australian co-production which was released in 2008. He also appeared in the independent New Zealand feature I'm not Harry Jenson.
Mitchell speaks fluent Te Reo Māori, and lent his support to the Maori Language Week campaigns in 2006 and 2008.
Mitchell has been known for his support of the Ponsonby Hero parade [now Hero Festival] featuring in the parade from 2001–03 and also dancing at the Salvation Hero party in support of HIV charities. His daughter Mila Rose Amaia Mitchell was born June 2009. His second daughter, Sophia Grace was born in 2010.