The Gladstone Branch proper, the part of the Gladstone Line west of the junction with the Morris & Essex at Summit, is The line primarily operates in the eastbound direction weekday peak hours, except for a small number of reverse peak trains.

(This shuttle train was later extended to provide bihourly service to Bay Street on the Montclair-Boonton Line).

The line is colored pale green on system maps and its symbol is a horse, a reference to the Grand National Hurdle Stakes steeplechase race held in the area.

The Delaware Lackawanna and Western Railroad (DL&W) leased the line on November 1, 1882 as a branch of the Morris and Essex.

The Passaic and Delaware Extension Railroad was chartered in 1890 and opened later that year, extending the line to its current terminus in Gladstone, New Jersey.

The branch received severe damage from Hurricane Sandy on October 29–30, 2012, especially to the catenary and signal system, causing a suspension of service for one month.

Gladstone service resumed on Monday, December 3 with electric Midtown Direct trains to Penn Station and diesel-powered trains to Hoboken; full electric operation was impractical until substation damage near Hoboken was repaired in early 2013.

The Gladstone Branch parallels the Amtrak Northeast Corridor and PATH lines and Interstate 280 (I-280) for a short distance here.

It enters the newly renovated Newark Broad Street station, which features two high platforms serving all three tracks.

After passing the abandoned station at Grove Street, now the location of Green interlocking, the line crosses the Garden State Parkway and reaches East Orange, which is situated on a viaduct.

The line then curves southward over Interstate 280, passing past Highland Avenue and Mountain Station.

The next station is South Orange, an elevated structure with two platforms and three tracks, near Seton Hall University.

There used to be a siding for the General Chemical Company plant just west of the Snyder Avenue crossing, but this was removed between 2018 and 2019.

The line crosses Plainfield Avenue and enters Berkeley Heights station, which also contains a siding for parking equipment.

Until recently, the original semaphore signal from the DL&W years used to sit atop the Basking Ridge station over the platform, one of the last vestiges of the previous operator of the line.

At Whitenack Road is the site of the former Mine Brook station, a flag stop in the line's DL&W years.

Just west of the station near the freight house, the track splits in two again to allow eastbound and westbound trains to pass each other.

The apparent last freight train made its run on November 7, 2008; however, seven months later the facility began receiving shipments again, on June 19, 2009.

In addition to the NJT Summit traction substation, three other switching facilities are located along the line.