Lynch starred in the indie drama My Name Is Emily, which premiered at the 2015 Galway Film Fleadh to critical acclaim.

She has been involved with several non-profit organisations and launched both a vegan-themed podcast and the cruelty-free cosmetics brand Kinder Beauty Box.

[1] She was educated at Cartown National School in Termonfeckin until June 2004 and then moved to Our Lady's College in Drogheda,[2][7] where her father was the deputy principal.

[9][10] In 2008, she studied speculative fiction and drama at the Centre for the Talented Youth of Ireland, a summer school for gifted teens, in Glasnevin.

[17] 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.

[43][44] The Seattle Times wrote that Lynch "continues to be all-that-and-a-radish-earring as the ever-wafting Luna Lovegood,"[45] and Orlando Sentinel named her as "maybe" one of his "favourite players in the finale.

Harry Potter author J. K. Rowling gave a speech during the premiere of Deathly Hallows – Part 2 in London, where 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.

[48] Rowling has maintained that, of all the actors in the film series, Lynch had the most influence on how the respective character was subsequently written; in 2012, she told Charlie Rose that when writing the final books, "I saw her.

[50][51] She was cast in the 2013 indie crime drama film Monster Butler, based on the life of British serial killer and thief Archibald Hall.

[54] Lynch appeared alongside Harry Potter co-stars James and Oliver Phelps in Danny and the Human Zoo, released on BBC One in August 2015.

[55] Lynch starred as the titular character in the Irish independent drama My Name Is Emily, written and directed Simon Fitzmaurice.

[61] In November 2017, it was reported that she would star in the independent drama Indigo Valley, directed by Jaclyn Bethany,[62] but was forced to drop out of the project due to scheduling conflicts[63] and was replaced with Rosie Day.

[67] 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.

[69] Lynch lent her voice to Nickelodeon productions Middle School Moguls in 2019 and Rise of the Teenage Mutant Ninja Turtles in 2020.

[72] Along with her Harry Potter costars Bonnie Wright, Devon Murray, and Mark Williams, Lynch attended the 2021 Comic Con Stuttgart, where the four of them did met-and-greets with fans.

[81][82] Lynch voiced the lead character in the 2024 animated film My Freaky Family (working title Being Betty Flood).

[83] Her next lead role will be in the satirical film Influenced!, a modern take on Oscar Wilde's The Picture of Dorian Gray.

[85] It was announced in 2023 that Rupert Friend had replaced Gillen while Lynch was cast as Lucia,[86] reprising a role she previously performed in a short film and a rehearsed stage reading.

"[87] Lynch has participated in charity work, including with the Multiple Sclerosis Society of Ireland, in which she launched their MS Readathon fundraiser in 2010.

[92] Lynch contributed an essay to the 2018 book Feminists Don't Wear Pink and Other Lies, curated by Scarlett Curtis, whose royalties went to the United Nations charity Girl Up.

[96] 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.

[107] In June 2018, she narrated a short film by the Humane Society International against the dog and cat meat trade in Asia.

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".

[109] In November 2017, Lynch founded the podcast The ChickPeeps, co-hosted 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.

[96] Lynch started The ChickPeeps with the intention of running "a bit more vulnerable and human [vegan podcast] that feels like you're hanging out with friends... where we have a laugh, maybe we learn some things, maybe we ask some questions".

[81][82][111] When J.K. Rowling posted a series of tweets on Twitter about the transgender community starting in 2020, she received significant criticism, including from most Harry Potter cast members.

[5] Lynch has worked to promote healthy self-esteem and body image in young girls because of her previous experiences with the eating disorder anorexia nervosa.

[122] She wrote an essay, "Why the Body Bind is My Nightmare", where she described her emotional struggle with her appearance and how she managed to overcome it through allusions pertaining to the Harry Potter series.