The line opened for service on September 14, 2024, and cost $133.4 million to construct; it features several sections with bus lanes and transit signal priority.

The G Line crosses Broadway, with a station connecting to the First Hill Streetcar, and passes the campus of Seattle University before transitioning to mixed traffic east of 15th Avenue.

The route continues into Madison Valley, serving several curbside stations, before terminating at Martin Luther King Jr. Way near the Washington Park Arboretum.

[12] Metro was unable to find another North American manufacturer willing to build articulated trolleybuses that could handle the very steep grades on the westernmost portion of the line (18–19%).

[18] While other routes were given feasibility studies for streetcars, as part of a new municipal system, Madison Street was considered too steep to support rail transit.

[19][20] A design concept for the service was first presented for public comment in 2014, featuring two options for the eastern terminus, at 23rd Avenue or Martin Luther King Jr Way (MLK Way).

A public survey was conducted and found higher support for the MLK Way terminus, as well as preferences for station locations and transfers to other transit routes.

[22] Residents of a condominium building on the line opposed the construction of a traction power substation that would be needed for the trolleybuses, citing possible health risks from exposure to electromagnetic fields.

[23] Portions of properties along the route were acquired for construction of wider sidewalks and platforms, including the patio space of queer bar Pony.