He made his Aviva Premiership A League debut for Gloucester against the Sale Jets in January 2015 at the age of 18.[citation needed]
On 27 May 2015, Protheroe signed his first professional contract with Gloucester Rugby, despite attraction from other top Premiership clubs.[4] However, he left early by mutual agreement to join local rivals Bristol Rugby in the RFU Championship from the 2017–18 season.[5]
On 22 February 2015, Protheroe was selected for England U18s, qualifying for England age group sides by virtue of playing for an English club, despite having no family or residential qualification for England.[6] He produced a man-of-the-match performance in their 21–5 victory over France.[7]
On 26 February 2020, the Ospreys announced the signing of Protheroe from Bristol for the 2020–21 season.[8]