The son of a real estate agent, Weir was born in Sydney on August 21, 1944. After giving his father's business a try, he spent time traveling around Europe. Upon his return to Australia, Weir secured a job with the Commonwealth Film Unit, where he learned his craft on the sets of documentaries and educational films. He made his directorial debut in 1971 with Three to Go, an effort that went largely unnoticed by audiences and critics alike. His next feature, The Cars That Ate Paris (1974), was a horror comedy with decidedly black overtones and fared considerably better than his previous effort. Even more successful was Weir's adaptation of Picnic at Hanging Rock the following year. A haunting, surreal tale of schoolgirls gone missing in the outback, it received critical acclaim and became something of a cult classic. The same could be said of The Last Wave (1977), a similarly dreamlike murder mystery set in Sydney.

Weir first achieved international recognition (as well as an Australian Film Institute Best Director award) with Gallipoli in 1981. Starring a then relatively obscure Mel Gibson as one of two friends who go off to fight in World War I, it was hailed by international critics and established Weir's reputation outside of Australia. His reputation was further enhanced the next year with The Year of Living Dangerously, which also starred Gibson, as well as Sigourney Weaver. A romance set against the backdrop of the toppling of Indonesia's Sukarno regime in 1965, it was screened in competition at the Cannes Festival and proved to be Weir's first big commercial success.

With Witness (1985), Weir made his first excursion onto American soil, documenting a culture clash viewed from the eyes of a wounded Philadelphia cop (Harrison Ford) recovering from his injuries on the farm of an Amish family. Aside from establishing Ford as an actor capable of more than big-budget action flicks, Witness earned Weir his first Best Director Academy Award nomination. Less successful was his next film and second collaboration with Ford, an adaptation of Paul Theroux's The Mosquito Coast (1986). Despite strong material and an excellent cast that included Ford, Helen Mirren, and River Phoenix, the film failed to find success with either critics or audiences.

Weir rebounded in 1989 with Dead Poets Society. Doing for star Robin Williams what Witness had done for Ford, the film earned Weir his second Oscar nomination, won a French César for Best Foreign Film, and became a stock reference point in the teen angst film lexicon. Weir subsequently went in a different direction altogether with Green Card. A romantic comedy starring Gérard Depardieu and Andie MacDowell, it was largely deemed a pleasant, if inconsequential, excursion, although it did earn Weir a Best Original Screenplay Oscar nomination.

After a disappointing reception for Fearless, a 1993 film starring Jeff Bridges as an airplane crash survivor trying to make sense out of his life, Weir rebounded strongly in 1998 with The Truman Show. Starring Jim Carrey in his first serious role as a man trapped in a TV show about his own artificially constructed life, the film was a surreal, darkly humorous take on contemporary society's obsession with the media and celebrity. It was embraced by both critics and audiences, earning Weir his third Best Director Oscar nomination, as well as a host of other honors.

Weir took five years to follow up The Truman Show, but when the Napoleonic-era navel epic Master and Commander: The Far Side of the World came along in 2003, it was greeted with many rapturous reviews and earned multiple Academy Award nominations, including Best Picture and yet another Best Director nod for Weir. The film starred Weir's fellow Aussie Russell Crowe.