Donnell began playing mini rugby for Winchester RFC and has represented England at under-18s and also under-20s level.
He joined London Irish’s academy at 16 and went onto captain the Exiles’ Under-18s. Donnell made his senior debut at just 18, in the Anglo-Welsh Cup and quickly became a regular squad member.
The athletic back-row was approaching 50 appearances when Irish went into administration and found himself at Gloucester.
He moved to Cardiff midway through the 2023-24 season and has established himself as a first team regular.