Friends said the Oscar nominee passed away peacefully in hospital in Shropshire Sunday. He is survived by his wife, Jacqui, his son, Will, and daughter, Lily, reports guardian.co.uk.
Postlethwaite was once described by Spielberg as "probably the best actor in the world today".
The craggy-featured actor received an Oscar nomination for his performance as Guiseppe Conlon in the 1993 film "In The Name Of The Father", about the wrongful convictions of the Guildford Four.
His notable films included the 1996 film "Brassed Off" in which he played the leader of a colliery band in a Yorkshire community devastated by mine closures. The film was a favourite of the former British deputy prime minister John Prescott, and became the inspiration for a coalfield regeneration programme.
Postlethwaite also played the menacing criminal mastermind Kobayashi in the 1995 hit film "The Usual Suspects".
In recent years he became known as much for his political activism. He was the front man in the climate change film "The Age of Stupid", arriving at the 2009 London premiere on a bicycle.
After the film's release he threatened to hand back the OBE he was awarded in 2004 over the government's controversial decision to give the go-ahead for Kingsnorth coal-fired power station in Kent.
He also adapted his home to become environmentally responsible, installing a wind turbine and other features.
In 2003, he marched against the war in Iraq and was a vocal supporter of the Make Poverty History campaign.
Born in Warrington, he had originally planned to be a priest. He later became a teacher but eventually took to the stage, beginning his career at the Everyman theatre in Liverpool.
In 2008 he returned to play the lead in "King Lear", a role he had always wanted to play. The performance was one of the highlights of Liverpool's year as the European Capital of Culture.
