Shaw clocked four hours, 27 minutes and 21 seconds for the half ironman event, which took place in hot conditions.
It followed on from his victories at the Taunton and Wincanton triathlons and from qualifying for the 2018 Ironman 70.3 World Championships after finishing second in his age category at the Staffordshire Ironman 70.3.
Sunday’s success also ended a good sporting week for Shaw, who had won the Ermington Time Trial in a new course record time on Wednesday night and then broke the Plymouth Corinthian Cycling Club 10 mile record on Thursday evening.
He will be hoping to continue his success this coming weekend when he competes in the Plymouth Triathlon at Mount Batten.
Shaw will be hoping conditions will be a bit cooler for the Plymouth event than they were at Weymouth on Sunday.
He admitted the heat was an issue on the run on Sunday and so took it slowly. His main focus this year is the Ironman 70.3 World Championships in South Africa at the start of September.
The city teacher clocked 25.08 minutes for the swim on Sunday, 2:14.59 for the cycle and 1:44.55 for the run.
Royal Navy athlete Emily Newton was second women overall in 5:12.54.
Plymouth Harriers’ Elizabeth Coombes was fourth in her age category in a time of 6:12.50, while Tavistock Tri Club veteran Lindsay Hobbs was seventh in her section in 6:51.45.