Hallard has been acting professionally since 1999, when he appeared in a production of Seven Brides for Seven Brothers at the Battersea Arts Centre. Since then his roles have included Sordo in Scenes from an Execution at the Royal National Theatre, Lysander in A Midsummer Night's Dream, Bill Taylor in the Michael Frayn farce Donkeys' Years, Jack Worthing in The Importance of Being Earnest and Judah in Joseph and the Amazing Technicolor Dreamcoat. His recent work includes the National Theatre production Great Britain by Richard Bean in the ensemble multi-character role of Jimmy the Bins/ St. John/Felix. In 2015 he played the leading role of Alan Turing in the UK premiere of the Snoo Wilson play Lovesong of the Electric Bear at the Arts Theatre.