The joint venture will be responsible for completing the detailed design, construction and planting of the £175m bridge over the Thames.
Engineering firm Bouygues TP and Italian steel manufacturer Cimolai have been working with the trust since April 2015 when they were appointed for preconstruction services, following a formal competitive procurement process. Since then they have been working on finalising the technical proposals for the delivery of the project.
The construction contract was intended to be awarded in September 2015, but the process was hit by delays after Lambeth Council suspended negotiations over concerns around public funding. Negotiations were resumed after the Garden Bridge Trust agreed that £20m of the TfL funding for the bridge would be treated as a loan, to be paid back over a 50-year term.
Around 80 per cent of Lambeth Council's pre-commencement planning conditions have now been approved, following a planning committee meeting last week. Other conditions relating to the commencement of particular construction works still need to be discharged although the trust says it already has approval for two out of seven of these.
The trust said lease negotiations are continuing over the land required for the South Landing, which is held in a long-term trust by Coin Street Community Builders. Opponents of the bridge have recently directed their efforts towards convincing the Coin Street housing trust to deny the bridge permission to build on the land.
Opponents are also awaiting the GLA Oversight Committee's report on its investigation into the bridge design procurement process, which will be released on Thursday (18 March).
Lord Mervyn Davies, chairman of the Garden Bridge Trust, said the bridge is "a reality", with the trust on course with its fundraising targets and meeting the requirements of its planning conditions.
To mark the signing of the construction contract the trust has released a new film celebrating London and its people. Construction work on the bridge is planned to commence in the summer of 2016 and to be completed in late 2018.