Researchers say the findings should provide confidence in insulin pumps to help the one-third of patients who struggle to control blood sugars with injections.
But an expert warned that it remained unclear whether they would be value for money for the NHS.
Previous studies had returned mixed results on the efficacy of insulin pumps but the OpT2mise trial by researchers in France showed a clear benefit.
The study in The Lancet involved 495 adults aged 30-75 with poorly controlled type 2 diabetes, who were helped to optimise daily insulin injections for two months prior to the study.
After this period, researchers randomly assigned the 331 adults with HbA1c levels still above 16.5mmol/L to continue multiple daily insulin injections or use an insulin pump.
Patients using an insulin pump saw HbA1c levels fall by 1.1mmol/L more than those using injections.
More than half (55%) of patients using pump therapy reached the target HbA1c level of 10.1mmol/L compared with just 28% of injecting patients.
Those on pump therapy also spent three hours fewer each day in hyperglycaemia. By the end of the study, insulin doses were 20% lower in patients using pumps.
Lead author Professor Yves Reznik from the University of Caen Côte de Nacre Regional Hospital Center in Caen, France said: 'Pumps enhance effective insulin absorption and increase insulin sensitivity thanks to the continuous daily subcutaneous insulin delivery.
'Our findings open up a valuable new treatment option for those individuals failing on current injection regimens and may also provide improved convenience, reducing the burden of dose tracking and scheduling, and decreasing insulin injection omissions.'
In an editorial, Dr Pratik Choudhary from King’s College London said: 'OpT2mise provides a compelling case for the clinical effectiveness of insulin pump treatment in type 2 diabetes, suggesting that it can help improve glycaemic control in this difficult-to-treat group of patients who are unable to achieve glucose control despite increasing doses of insulin. However, cost effectiveness of pumps in different healthcare systems will need to be evaluated.'