Fleck Byrne's first acting job was in Liverpool in the play Antony and Cleopatra opposite Kim Cattrall. In 2014 Byrne could be seen as Harry Abrams, an assistant of the psychological researcher Joseph Coupland, in the horror movie The Quiet Ones. In 2016 he played Ruby in the movie Tiger Raid. In 2017 he starred as Daniel Marney in eight episodes of Harlots, a drama series about Georgian-era brothels, and the women working there. Fleck Byrne's character Daniel falls in love with the madam of a low-class brothel. Later in 2017 he starred opposite Jackie Chan and Pierce Brosnan in The Foreigner. Fleck Byrne played Brosnan's nephew Sean Morrison, a former British royal navy officer. He later stated that up to then this was one of the best and most challenging experiences he had ever had. He had to train with a stunt team to fight martial arts and get into the mind of a hit-man. As he enjoyed martial arts so much he continued to train it after the film was finished with a personal trainer in London. Fleck Byrne also worked as an actor, writer and producer in the short films Inbox and Bodies. Bodies was set in his hometown Kilkenny. It is about the relationship of two funeral directors who struggle to stay connected to life. Inbox was released with help of the crowdfunding website Kickstarter.
