The publisher will bring its Daily Record, Sunday Mail and Dumfries and Galloway Standard newspapers to the partnership as a complement to Macmillan Media's TV news operation, which currently produces GMTV's bulletins for Scotland and Northern Ireland.
The joint bid will aim to secure a portion of government funding allocated for the new independently funded news consortia (IFNC) scheme. The Scottish pilot will get underway in April 2010, alongside similar trials in Wales and Tyne Tees and Border in England.
Under the Trinity/Macmillan proposal, news bulletins would be produced entirely from Dumfries and Galloway and the Borders, rather than the current service origin of Gateshead. Local coverage would be further boosted by video journalists based in towns and villages throughout the region.
The new service would also incorporate its own dedicated website and give access to multimedia training for a range of community groups.
"This will give communities in the south of Scotland back their voice on TV," said Trinity Mirror chief executive Sly Bailey. "With our partners Macmillan Media, we aim to deliver an enhanced, low-cost model for the local TV news of the future."
Macmillan Media owner Michael Macmillan added: "Our combination of multimedia journalism skills will deliver the TV news service that the south of Scotland demands and deserves."
Trinity Mirror has also partnered with Ten Alps and the Press Association to launch a separate bid for the Tyne Tees and Border pilot scheme.