He then made the move to London to pursue a career in musical theatre, securing a role in the West End production of Les Misérables.
On 3 October 2010, Donnelly played the role of Courfeyrac in the 25th Anniversary Concert of Les Misérables at The O2 Arena in London.
On 20 August 2013, it was confirmed that Donnelly would originate the role of Deco in the West End Musical The Commitments[5] from 21 September.
[6] The following year Donnelly began playing the role of Huey in Memphis from 9 October 2014 for which he was nominated as Best Actor in a Musical in the 2015 Olivier Awards[7] On 23 April 2015, it was announced that Donnelly would play Charlie in the West End production of the musical Kinky Boots,[8] at the Adelphi Theatre.
[15] On 31 October 2023, Donnelly rejoined Les Misérables in the new West End production at the Sondheim Theatre reprising his role of Valjean for 15 weeks.
Donnelly performed the role in the UK, Australia, Sweden, the Netherlands, Italy, the United Arab Emirates, Denmark, Norway, Switzerland, and Luxembourg.
[17] Donnelly is set to perform at the 10th-anniversary concert of the Made in Dagenham musical at the London Palladium in March 2024.