[8] Groundbreaking for the line occurred on August 31, 2011, at a ceremony in Olde Town Arvada where US Transportation Secretary Ray LaHood announced the approval of a $1 billion grant to fund the project.

After RTD solved timing issues with the gates, subject to Federal Railroad Administration approval, the G Line opened without flaggers and quiet zones in place on April 26, 2019.

Testing began in January 2018 and the state's Public Utilities Commission approved the automated gates in March.

[11][12] Pending FRA approval of the crossing systems in December 2018, the agency claimed it could begin operations as late as Q1 2019.

It runs on a railroad right-of-way north sharing track with the B Line until Pecos Junction station after which the two routes diverge.