Henry Ian Cusick Chavez was born in Trujillo, Peru to a Peruvian mother and a Scottish father. He is fluent in both English and Spanish, and grew up in Trinidad and Tobago where he attended Presentation College and Scotland, moving to the latter at the age of fifteen. He was raised Roman Catholic. Cusick spent 6 months at the Royal Scottish Academy of Music and Drama in Glasgow before being asked to leave for drug abuse and attendance issues. He then joined the Citizens' Theatre. Cusick and wife Annie are parents to three sons, Elias, Lucas and Esau. The couple was married in a civil ceremony following fourteen years of cohabitation on July 15, 2006.

His first leading roles there included Dorian Gray in The Picture of Dorian Gray with Rupert Everett, Hamlet in The Marovitz Hamlet with Helen Baxendale, and Horner in The Country Wife.

His performances as Torquato Tasso in the Edinburgh International Festival production of Torquato Tasso, and Creon in the Citizens' Theatre production of Oedipus earned him a special commendation for the Ian Charleson Award 1995 for outstanding performance by a young actor in a classical theatre role. He was nominated for an Emmy for his guest role as Desmond on Lost.

He has joined the main cast of the TV show Lost as Desmond and appeared in two episodes of season 5 of 24.

He lives in Oahu, Hawaii with his wife, Annie, and their kids.

• His mother is Peruvian and his father is Scottish. He was raised in Trinidad and Tobago and Scotland.
• He was kicked out of The Royal Scottish Academy of Music and Drama before joining the Glasgow Citizens Theatre where he performed for a number of years. He also performed with The Royal Shakespeare Company, Royal National Theatre, The Almeida, Liverpool Playhouse, Babel Theatre Company, 7:84 Theatre Company (Scotland) to name a few...
• He auditioned for Lost (2004) by putting himself on DVD in London and sending it off to LA.
• Special commendation for the Ian Charleson Award 1994 (Best performance by an actor under 30 in a classical role).
• Has three sons: Elias, Lucas and Esau.
• Speaks fluent Spanish.