Simmonds made his full debut for Exeter on 4 March 2018 against Saracens and was named man of the match.[4]
The following week he kicked the winning penalty as Exeter beat the Newcastle Falcons to advance to the Anglo-Welsh Cup final.[5]
In the final, which had been rearranged to March 30 due to snow, Simmonds kicked 13 points as the Chiefs won the cup 28–11 against Bath Rugby.[6] The previous season he had played in the Anglo-Welsh Cup final but Exeter lost to Leicester Tigers on that occasion.[7]
Simmonds led Exeter on the pitch in the delayed final of the 2020 Champions Cup.[9] Simmonds is the youngest player to captain a side to victory in the final of the European Cup.[10] He also won 'Star of the Match' for his performance in that game[10] and kicked 5 successful kicks out of 5 attempts. He was top points scorer in the 2019–20 European Rugby Champions Cup.
In May 2023, it was confirmed Simmonds was signing for the French side, Pau, after the implementation of new financial restrictions in the Premiership resulted in a number of players leaving Exeter Chiefs.[11]