Reffell began his junior career at his local club Pencoed RFC aged 4.[3] He was part of the Ospreys under 16s[2] and joined Leicester aged 15.[3]
Reffell made his debut for Leicester Tigers on 10 November 2017 in a 33–31 defeat against Bath at the Rec in the Anglo-Welsh Cup.[4][5]
In March 2020, Reffell won the Premiership Rugby Cup Breakthrough Player award for his performances in that year's competition.[6]
His form for Leicester in the 2020–21 season lead to speculation that he was in contention to be capped by either England or Wales, but he remained uncapped.[7] He was named man of the match by the Leicester Mercury following his performance in Tigers' win against Gloucester on 24 September 2021.[8][9]
His form continued into the next season, earning plaudits as he scored twice in the win against Harlequins on 16 October 2022.[10] On 27 November 2022 he was again named player of the match, scoring Leicester's fourth try in the win over London Irish.[11]
In June, Reffell started the 2022 Premiership Rugby final as Leicester won 15-12 against Saracens.[12]
Reffell scored the winning try as Leicester beat Exeter Chiefs on the opening day of the 2024-25 Premiership Rugby season.
After another spell of good form, in May 2022, Reffell was named in the Wales squad for their summer tour to South Africa.[15] On 2 July 2022 Reffell made his debut for Wales in their 32–29 defeat to South Africa at Loftus Versfeld in Pretoria.[16] The following match on 9 July 2022 saw him win the man of the match award, as Wales beat South Africa 13-12 for their first ever win against South Africa in South Africa.[17]
Reffell kept his position into the 2022 Autumn Internationals, starting against New Zealand.[18] Reffell was injured during the match, and played no further part in Wales's autumn campaign.[19]