A member of the Gyllenhaal family and the son of director Stephen Gyllenhaal and screenwriter Naomi Foner, Gyllenhaal began acting as a child with a screen debut in City Slickers (1991), followed by roles in A Dangerous Woman (1993) and Homegrown (1998).
His breakthrough performance was as Homer Hickam in October Sky (1999) and he garnered an Independent Spirit Award nomination for Best Male Lead for playing the title character in the indie cult hit Donnie Darko (2001), in which he played a psychologically troubled teenager alongside his older sister, Maggie Gyllenhaal.
He subsequently appeared in another indie film, The Good Girl (2002) and the climate fiction-disaster film The Day After Tomorrow (2004), portraying a student caught in a cataclysmic climate event.
Gyllenhaal's father, who was raised as a Swedenborgian, is of Swedish and English descent, and is a descendant of the Swedish noble Gyllenhaal family.
On his 13th birthday, Gyllenhaal performed a "bar mitzvah-like act, without the typical trappings", volunteering at a homeless shelter because his parents wanted to give him a sense of gratitude for his privileged lifestyle.
As a child, Gyllenhaal was regularly exposed to filmmaking due to his family's deep ties to the industry.
He made his acting debut as Billy Crystal's son in the 1991 comedy film City Slickers.
For his performance in Brokeback Mountain, he received critical acclaim and won the BAFTA Award for Best Actor in a Supporting Role and was nominated for the Screen Actors Guild Award for Outstanding Performance by a Male Actor in a Supporting Role, the Satellite Award for Best Supporting Actor – Motion Picture, and the Academy Award for Best Supporting Actor.
Gyllenhaal received further recognition for roles in Zodiac (2007), Brothers (2009), Prince of Persia: The Sands of Time (2010), Love & Other Drugs (2010), for which he was nominated for a Golden Globe Award for Best Actor – Motion Picture Musical or Comedy, Source Code (2011), End of Watch (2012), Prisoners (2013), Nightcrawler (2014), and Southpaw (2015).
For Nightcrawler, his performance was widely acclaimed and received rave reviews from critics and he was nominated for the Golden Globe Award for Best Actor – Motion Picture Drama, the Screen Actors Guild Award for Outstanding Performance by a Male Actor in a Leading Role, and the BAFTA Award for Best Actor in a Leading Role.
Actress Maggie Gyllenhaal, his older sister, appeared with him in the film Donnie Darko.
His parents did not allow him to appear in the 1992 film The Mighty Ducks because it would have required his leaving home for two months.