Ioan was born in Cardiff, Wales, UK. His parents, Peter and Gillian Gruffudd, were educators.

He has a brother, Alun, who is two years younger and a sister, Siwan, who is 7 years younger.

He attended the Royal Academy Of Dramatic Arts from 1992 to 1995, but was then cast as "Poldark" in the popular British TV series Poldark.
Man and Boy (2002): £ 150,000
Shared a flat in London with old friend and fellow Welsh actor Matthew Rhys. He played the oboe in the South Glamorgan Youth Orchestra for several years. He learned Yiddish for his role in the film Solomon & Gaenor. Had the honor of lighting the National Millennium Beacon for Wales in Cardiff City Centre for the New Year's Eve 2000 celebration. Won the BBC Radio Cymru Showbusnesan Award for Best Actor (March 28, 2001). Graduated from London's Royal Academy of Dramatic Art (1995). An Associate Member of RADA. Lives in Los Angeles (for 2 years as of July 2004). First language is Welsh. His name is pronounced "Yo-wahn Griffith". Parents were teachers. Grandparents ran a local amateur drama society in Cardiff. Was already an accomplished singer and oboist by the age of 13. Became a professional actor at the age of 13 with his role in the Welsh soap opera Pobol y Cwm ("People of the Valley"). Best friend is Matthew Rhys. Has a younger brother, Alun and a younger sister, Siwan. Living with fellow British actress Alice Evans in Los Angeles (July 2005). Was invited to and accepted into Gorsedd y Beirdd Ynys Prydain (the [Welsh] Bardic Order of Great Britain) at the highest rank in the National Eisteddfod at Meifod in 2003, with the bardic name "Ioan". In addition to playing Mr. Fantastic/Reed Richards in Fantastic Four, he provided the voice of Mr. Miracle/Scott Free for the animated Justice League series. Ironic, given that Mr. Miracle is owned by DC Comics, rival of Marvel Comics, which owns the Fantastic Four, and both characters were created by the late Jack Kirby. Met his girlfriend, actress Alice Evans, on the set of 102 Dalmatians, although at the time she was romantically involved with Pablo Picasso's grandson, Olivier. Best friends with Jamie Bamber who played "Archie Kennedy" on "Hornblower" and is currently playing Lee "Apollo" Adama on Battlestar Galactica. Best friend is Matthew Rhys. Has a younger brother, Alun & a younger sister, Siwan. Ioan and his fiancée, Alice Evans, are planning their wedding for September, 2007.