"Downer has a strong track record of delivering here in Australia, and around the world, so Queensland's future fleet is in good hands," Queensland State Premier Annastacia Palaszczuk said.

The trains are to be manufactured as part of the Queensland Trains Manufacturing Programme (QTMP) which is said to be the biggest rail investment ever made by the state.

Negotiations to finalise the agreement had been held since Downer was announced as the preferred supplier for the programme earlier this year.

All the trains are expected to comprise six carriages and be operational in time for the Olympics and Paralympics in 2032.

"These 65 new trains will support South East Queensland's population boom, as well as Cross River Rail and the Brisbane 2032 Olympic and Paralympic Games," insisted Queensland Assistant Minister for Regional Roads and Train Manufacturing Bruce Saunders.

The Queensland Government expect the project to support 800 construction and manufacturing jobs in the region.

A new train manufacturing plant is to be built at Maryborough in the Fraser Coast region some 250 kilometres North of Brisbane. 

"Queensland trains should be made in Queensland," Palaszczuk declared.

The agreement also includes the provision of a facility for train maintenance and stabling at Ormeau, midway between Brisbane and the Gold Coast.

Downer is also to be responsible for maintaining the fleet for an initial term of 15 years and a maximum of 35 years under the terms of the deal.

"Downer is proud to be part of this project, which will change the way people travel around South East Queensland as well as maintain and enhance local rolling stock manufacturing capability in Queensland," a Downer Group statement said.

The new trains will be more accessible for people with a disability, with the addition of train boarding bridges and electronic levelling controls to allow easier access for wheelchairs.

The Brisbane Olympics are set to open on July 23 2032.