The Orica-Scott star burst from the peloton to seal stage three by half a wheel-length from his nearest rival and add to his win in the opening sprint stage on Sunday.
Tour of Britain: Caleb Ewan sprints to victory on stage three
It proved another eventful day for Boasson Hagen, who was stripped of victory in stage two for irregular sprinting having put on the leader's green jersey on the podium.
Frenchman Philippe Gilbert (Quick Step Floors) had attempted to take the race out of the sprinters' hands by charging clear two kilometres from the line, but he was swallowed up in the final 50 metres.
Caleb Ewan claimed victory on stage three of the Tour of Britain
Image credit: PA Sport
Ewan told Cycling News: "I was a bit disappointed after yesterday, I was boxed in during the sprint so I never got to open up [my sprint].
"Luckily the team still backed me 100 per cent, and we rode like we were going for the win straight from the start."
Ewan's stage win means he takes back the overall lead from Team Sky's Elia Viviani heading into Wednesday's fourth stage from Mansfield to Newark.