Lynch credits her being cast in the Harry Potter films to the obsession she had with the Harry Potter book series. At age 11, during the release of the fifth book Order of the Phoenix in June 2003, she was hospitalised and her family consulted with the book’s publisher and the hospital. Lynch then was allowed to leave for an hour and collect a signed copy of the book. While some have stated that her prior correspondence with J. K. Rowling was a major contributing factor behind the casting decision, this theory has been debunked by both Lynch and Rowling, confirming that Rowling was unaware of Lynch being cast in the role of Luna Lovegood until the producers mentioned Lynch’s name. Lynch got the role by reading about the casting call on one of the many Harry Potter fan sites and going to the open audition.

In January 2006, Lynch auditioned at a casting call in London for the role of Luna Lovegood in Harry Potter and the Order of the Phoenix, the fifth film in the series adapted from the books. After auditioning against 15,000 other girls, and a subsequent screen test with lead actor Daniel Radcliffe, she was cast at the age of 14. Producers were impressed with her affinity for the character; David Heyman said: “The others could play Luna; Evanna Lynch is Luna.” Although uninvolved in the casting process, Rowling believed that Lynch was perfect for the role. She had never acted professionally before the Harry Potter series, her experience having been limited to school plays. Harry Potter and the Order of the Phoenix was Lynch’s debut screen performance in 2007. The film was a box office hit, taking US$938 million worldwide, and garnered generally favourable reviews. Critics praised the performances of the supporting cast, often singling out Lynch for particular acclaim; A. O. Scott of The New York Times called her performance “spellbinding”, and Jane Watkins of Country Life said she “[brought] an appealing sweetness to her character that’s not so developed in the book”. She reprised her role as Luna in the film’s tie-in video game.

Lynch was born in Termonfeckin, County Louth, Ireland, the daughter of Marguerite and Donal Lynch. She has two older sisters, Emily and Mairead, and one younger brother named Patrick. As a child, Lynch read the Harry Potter series and became a fan, sending letters to the author, J. K. Rowling. She attended Cartown National School in Termonfeckin until June 2004 and then moved to Our Lady’s College in Drogheda, where her father was the deputy principal. In 2008, Lynch studied speculative fiction and drama at the Centre for the Talented Youth of Ireland, a summer school for gifted teens, in Glasnevin. While on the Harry Potter set, she was tutored for at least three hours a day. From September 2010, Lynch attended the Institute of Education to repeat her Leaving Certificate.

Harry Potter and the Deathly Hallows – Part 1, the first of two films adapted from the seventh and final Harry Potter book, was released in 2010. The film was a success at the box office and drew generally favourable reviews from critics. James Verniere of The Boston Herald commented that Luna “is still delightfully lunar,” while Simon Miraudo of Quickflix criticised the film commenting that “the delightful Evanna Lynch is brutally underutilized as the loopy Luna Lovegood”. She reprised her role in the film’s tie-in video game.

Her charity work includes participation with the Multiple Sclerosis Society of Ireland, in which she launched their MS Readathon fundraiser in 2010. Lynch is also a member of the Board of Advisors for the non-profit organisation, the Harry Potter Alliance (HPA). With the HPA, she has supported same-sex marriage in Maine, taken part in a webcast fundraiser, written an article about body image and contributed to a fundraising book.

The author of the Harry Potter series, J. K. Rowling, gave a speech during the world premiere of Harry Potter and the Deathly Hallows – Part 2 on 7 July 2011 in London, England. She stated that there were seven major cast members in the series, whom she referred to as The Big Seven, and she named Lynch as one of the seven members, along with Daniel Radcliffe, Rupert Grint, Emma Watson, Tom Felton, Matthew Lewis, and Bonnie Wright. Rowling has said that, of all the actors in the film series, Lynch has had the most influence on how her character was subsequently written. In 2012, she told Charlie Rose that when composing the final books, “I saw her. [She] got in my head. I even heard her voice when I was writing Luna.”

During her time appearing in the Harry Potter films, Lynch also made and helped design a number of fashion accessories for them. In August 2012 at Leakycon in Chicago she joined the cast of StarKid to play Luna Lovegood in a script reading of the third Harry Potter parody musical, A Very Potter Senior Year (the other two being A Very Potter Musical and A Very Potter Sequel).

Following her work in the Harry Potter films, Lynch went on to guest star as Princess Alehna (daughter of Taryn, played by Orla Brady) in the first season finale of the Sky1 television series Sinbad. She was also scheduled to play Fiona Carrick-Smith in the 2013 indie crime drama film Monster Butler. The film was to have been based on the life of British serial killer and thief Archibald Hall. The film was cancelled due to problems with funding. Lynch also starred in indie teen comedy G.B.F., which screened at the Tribeca Film Festival in New York in April 2013 and at the Frameline Film Festival in San Francisco on 30 June 2013.

In May 2013, it was announced that Lynch was to star in the British stage tour production called Houdini which performed at various theatres in the United Kingdom from 9 September 2013 to 12 October 2013. Lynch played the role of Bess Houdini, the wife and assistant of magician Harry Houdini.

In December 2013, it was announced that Lynch would play Theresa Bornstein in the independent crime thriller Dynamite: A Cautionary Tale. Filming for the production took place in New York City and was set to be filmed for eighteen days.

In September 2014, it was announced that Lynch would star in her first lead role as the titular character in the Irish-produced film My Name Is Emily, written and directed by a man battling amyotrophic lateral sclerosis. Filming began in Ireland that month and the film was released in 2015. In April 2017, it was announced she would star in a revival of Enda Walsh’s Disco Pigs for the London stage, which performed from 12 July-19 August 2017 at Trafalgar Studios. It was later transferred to Off-Broadway at the Irish Repertory Theatre and played from 5 January-4 March 2018.

In a 2014 interview, Lynch mentioned having a devout Catholic upbringing. “I stopped going to mass a few years ago, mainly because I disagree with the rules,” she said. “I don’t like anything that’s about punishing yourself and making you feel bad about yourself, and growing up I felt bad about indulging myself or doing anything for fun.”

In 2015, Lynch was the first person to sign the petition against live export in the On Cow tour, an event organised by Compassion in World Farming which visited eight cities in the European Union. Since then, she has joined many animal rights demonstrations and campaigns. In May 2018, Evanna Lynch and a journalist traveled to Kerala, India to observe the treatment of the endangered Asian elephant. In August, she and actor Peter Egan joined the organisation Save the Asian Elephants to hand in a 200,000-name petition to the Department for Environment, Food and Rural Affairs, demanding to ban the advertisement in the United Kingdom of “unethical Asian elephant related holidays abroad”, among other requests.

Lynch is an ambassador for J.K. Rowling’s charity Lumos. In 2016, Lynch and her Harry Potter co-star and fellow Lumos ambassador Bonnie Wright, travelled to Haiti to learn about why there are 30,000 children living in orphanages, and met children who had been rescued from terrible conditions and reunited with their families. Lynch stated about charity work for children and families, “Without families and without love, children can’t be children. The most important thing as a child is to be with your family. And you have to do everything you can to keep that family unit in place.”

In November 2017, it was confirmed that she would star in the independent drama Indigio Valley, directed by Jaclyn Bethany, but was forced to drop out from the project due to scheduling conflicts and was replaced by Rosie Day.

In 2017, Lynch narrated the short documentary iAnimal by Animal Equality, dealing with the dairy industry. The film received a nomination at the 2018 Raindance Film Festival. In June 2018, she narrated a short film by the Humane Society International against dog and cat meat trade in Asia.

In November 2017, Lynch founded the podcast The ChickPeeps, cohosted by Harry Potter and the Order of the Phoenix actor Robbie Jarvis, Surfers Against Sewage representative Momoko Hill, and Protego Foundation founder Tylor Starr. Its content is based on veganism and features discussions on diverse topics, often joined by prominent activists such as Ingrid Newkirk, Earthling Ed, and Victoria Moran, among many others.

In August 2018, she appeared in a cameo role in Jason Mewes’s directorial debut Madness in the Method.

On 12 September 2018, Lynch was announced as one of the celebrities to compete on season 27 of ABC’s Dancing with the Stars. Her professional partner was Keo Motsepe. Motsepe and Lynch made it to the show’s finale, making this the first time Motsepe had reached the finals, and they finished in third place.

In November 2018, Lynch co-founded, along with American actress Daniella Monet, the vegan and cruelty-free make-up and beauty care box Kinder Beauty Box. The subscription box, which started its monthly delivery in January 2019, was intended to “put ethical brands in the spotlight” and “overcome confusing jargon” used by big brands that test on animals. Kinder Beauty Box was conceived after Lynch and Monet discussed the difficulty they had looking for vegan beauty products. The products are curated by them, shipped in sustainable packaging and a portion of the sales goes to animal rights and environmental causes and benefits for vegan rights.

In March 2019, it was announced she would appear in the British premiere of the Argentinian play The Omission of the Family Coleman, written by Claudio Tolcachir, translated by Stella Feehily, directed by Laurence Boswell and presented by Ustinov Studio. It premiered at the Theatre Royal Bath on 28 March and will run through 27 April 2019. In July, Lynch revealed that she will star a vegan-themed short film entitled You Eat Other Animals late that year.

In a 2019 interview, Lynch said she “hated the blood [from raw meat]” as a child and, at the age of eleven, she became a vegetarian. In 2015, she turned to veganism for ethical reasons. Lynch said that her activism is mostly done “in my free time as a way to give back and a way to right the world.”

In October 2019, Lynch was announced as a Lovie Award winner for her activism. The committee stated that she “raises the bar for others in a position of fame to use the Internet in the most creative and accessible ways possible, to introduce new ideas to people that can truly change our world for the better.”

In February 2020, it was confirmed that Lynch will narrate the story The Fountain of Fair Fortune from the audiobook of The Tales of Beedle the Bard, based on J. K. Rowling’s novel of the same title. The audiobook released on 31 March 2020, in aid of Rowling’s charity, Lumos.