Silver medallist as part of the 4x200m Freestyle team at Glasgow 2014, Stephen was twice on the podium at Gold Coast 2018, winning bronze in both 4x100m and 4x200m Freestyle Relays. He also reached the final in both the 200m and 400m Freestyle.
He took Olympic silver at Rio 2016 as part of the 4x200m Freestyle Relay with the team, including fellow Scots Dan Wallace and Duncan Scott, setting a new British record in the final. The 2017 World Championships saw more relay success for Stephen, as the team went one better, taking the World title and breaking the British record once more en route to gold.