Sectornet has become the sixth software firm to sign up with Polaris to join imarket.
The IT provider joins Acturis, Cheshire
Data Systems, insurE-com, Misys and Software Solutions Partners in the imarket project.
Sectornet product development director Paul Methven said: "We supply many of the leading commercial brokers in the UK. They see imarket as an important part of their future trading strategy, and are keen to see us progress with this initiative."
The deal leaves Sirius as the only major software firm not to agree terms with Polaris, though negotiations between the two companies are understood to have reached final proposal stage.
Polaris managing director Martin McLachlan said: "We are very pleased to have agreed terms with Sectornet.
"By integrating the Sectornet and imarket solutions we will be able to deliver real business benefits and cost-savings to an important broking community."