The film had its world premiere at the Sundance Film Festival on January 23, 2016. It was screened in the Un Certain Regard section at the 2016 Cannes Film Festival. It was theatrically released on July 8, 2016 by Bleecker Street. It was chosen by the National Board of Review as one of the top ten independent films of 2016 and Mortensen was nominated for a Golden Globe for Best Actor and at the 70th British Academy Film Awards for Best Actor in a Leading Role and the Academy Award for Best Actor at the 89th Academy Awards.
Ben Cash, his wife Leslie and their six children live in the Washington wilderness. Ben and Leslie are former liberal activists disillusioned with capitalism and American life, and chose to instill survivalist skills, left wing politics, and philosophy in their children – educating them to think critically, training them to be self-reliant, physically fit and athletic, guiding them without technology, demonstrating the beauty of coexisting with nature and celebrating "Noam Chomsky Day" instead of Christmas.
Leslie is hospitalized for bipolar disorder and eventually commits suicide. Ben learns that his father-in-law Jack plans to hold a traditional funeral and burial, even though Leslie wished to be cremated. They argue over the phone and Jack threatens to have Ben arrested if he attends the funeral. He initially decides not to go and prevents his children from doing so, but then changes his mind, leading his children on a road trip into life outside the wilderness.
The family briefly stays at his sister Harper's house. She and her husband try to convince Ben that his children should attend school to receive a traditional education; Ben argues that his children are better educated than Harper's own children. Ben arrives at Leslie's funeral with his children and reads her will, which instructs her family to cremate her and flush her ashes down the toilet. In response, Jack has Ben forcibly removed.
Ben's children also start doubting their father and his parenting skills. His son Rellian accuses Ben of failing to treat Leslie's mental health. His son Bodevan accuses his father of failing to equip them for the real world by setting them up for a rude awakening when they grow up and shows him college acceptance letters from Ivy League schools for which Leslie had helped him apply. Rellian wants to live with his grandparents, who want to take custody of them. When Vespyr tries to climb into a window to "free" Rellian from his grandparents, she falls from the roof and narrowly avoids breaking her neck. Ben, shocked and guilty, allows Jack to take his children. The children soon bond with their grandparents, but decide to follow Ben again when he departs.
The children honor Leslie's wish and convince Ben to help them, exhuming her corpse, burning it in a self-made pyre and flushing her ashes down an airport toilet. Bodevan then leaves the family to travel through Namibia, while the rest settle on a farm. The final scene is the family around the kitchen table with their father, waiting for the school bus to arrive.
The idea of the movie started for Matt Ross as he began questioning the choices he and his wife were making as parents. From there he wondered what would happen if he were "completely present" in his children's lives, while noting that modern technology had made that difficult. In making the film Ross also took autobiographical bits from his own life, notably being raised in what he terms as "alternative-living communities" growing up.
Viggo Mortensen was cast in February 2014. That June, it was announced that George MacKay, Annalise Basso, Samantha Isler, Nicholas Hamilton, Shree Crooks and newcomer Charlie Shotwell had also been cast. Much of the rest of the cast joined that July and August.
Principal photography on the film commenced in July 2014, in Western Washington.
In July 2014, eOne Entertainment acquired international distribution rights to the film. In August 2014, it was announced that Bleecker Street would distribute the film in the United States. The film had its world premiere at the 2016 Sundance Film Festival on January 23, 2016. The film was released on July 8, 2016. The film was aired in the Un Certain Regard section at the 2016 Cannes Film Festival, with Matt Ross winning the Best Director prize.
Captain Fantastic grossed $5.9 million in the United States and Canada and $9 million in other territories for a worldwide total of $14.9 million.
On review aggregator website Rotten Tomatoes, the film has an approval rating of 83% based on 185 reviews, with an average rating of 7.1/10. The site's critical consensus reads, "Captain Fantastic's thought-provoking themes—and an absorbing starring turn from Viggo Mortensen—add up to an above-average family drama with unexpected twists." On Metacritic, the film holds a score of 72 out of 100, based on 36 critics, indicating "generally favorable reviews". It received a ten-minute standing ovation at Cannes.
Alonso Duralde of TheWrap gave the film a positive review, saying "The movie really belongs to Mortensen, who allows Ben to be exasperating, arrogant and impatient but also warm, loving and caring. He’s a tough but adoring father, a grieving widower and a passionate defender of his wife’s final wishes, and Mortensen plays all these notes and more with subtlety and grace". Peter Debruge of Variety gave the film a positive review, saying "Boasting half a dozen impressive youth performances alongside a leading role that takes full advantage of Mortensen’s own sensitive, back-to-nature spirit, Captain Fantastic easily ranks among the most polished and relatable of this year’s Sundance offerings."
One of the few negative reviews was from Peter Bradshaw of The Guardian. "There’s a meaty whiff of phoney-baloney in this fatuous and tiresome movie, replete with forced emotional crises and wrong notes, topped off with an excruciatingly unearned, sentimental ending. It's a low-cal version of Peter Weir’s 1986 movie The Mosquito Coast, starring someone who is essentially a cross between Charles Manson and Captain von Trapp."