Howle was born in Stoke-on-Trent, Staffordshire. He appeared as James Warwick on the E4 television series, Glue. He has since co-starred in the film, The Sense of an Ending (as the younger version of Jim Broadbent's lead character) and the miniseries The Witness for the Prosecution in the pivotal role of the defendant in a murder case, Leonard Vole.
He also appeared in the historical film Dunkirk, and starred with Saoirse Ronan in the 2017 drama film On Chesil Beach, an adaptation of Ian McEwan's novel. He appears in the film adaptation of Anton Chekhov's The Seagull and in the Netflix film Outlaw King.