Engineers have now fixed the 750 tonne bridge segment to the existing 1.7 mile deck span between Edinburgh and Fife.
Galliford Try is part of the four-company consortium that includes Hochtief, Dragados, and American Bridge of Pittsburgh in the US building the main motorway bridge over the Firth of Forth under a £790m contract.
The structure now becomes the longest three-tower, cable-stayed bridge in the world and also by far the longest to feature cables which cross mid-span.
This innovative design provides extra strength and stiffness, allowing the towers and the deck to be more slender and elegant.
Michael Martin, project director for Forth Crossing Bridge Constructors said: “This final deck lift is the culmination of a world class team effort stretching all the way back to the very first day of construction in 2011.
“The final “closure” is always one of the most significant milestones in any bridge construction programme. On a bridge of this magnificent scale, well, it’s more than a bit special. It is a real pleasure to pay tribute to the skill and dedication of everybody involved and to congratulate them on an outstanding achievement.
“We are now focused on completing the huge range of finishing works and bringing the Project to a successful conclusion.”
The Queensferry Crossing is due to open in May.