The segment in Downtown Baltimore is underground, while most of the line outside the central city is elevated or at surface grade.

The origins of the Metro SubwayLink lie in the Baltimore Area Mass Transportation Plan published in 1965, which envisioned six rapid transit lines radiating out from a central city loop.

[2] As the vision was translated into reality, the original concept was trimmed to a 28 mi (45 km) system in the Phase 1 plan, published in 1971.

On July 20, 1987, a 6.1 mi (9.8 km) addition extended the line from Reisterstown Plaza to Owings Mills in Baltimore County, with a portion running in the median of Interstate 795.

[5] When the system opened, it became the largest single user of Susan B. Anthony dollar coins in the United States.

[6] The installation of underground cellular service in the Metro SubwayLink tunnels began in September 2021 and was originally expected to be completed by June 2022.

[9] As of 2024, the fare prices for MTA buses, the Metro SubwayLink, and the Light RailLink travel are as follows:[10] Farebox recovery in the system is only 28%.

This is comparable to other similarly sized systems in the continental United States, but low by international standards.

In 1984, just months after Metro first started operating, many feeder routes were created that were given the designation of a letter (M, P, or R) followed by a number.

The cars, marketed by Budd as the Universal Transit Vehicle, are identical to those formerly used on the Miami Metrorail; the two agencies built their systems at the same time and saved money by sharing a single order.

The cars are being built in Florida by Hitachi Rail Italy, and will be similar in appearance to those purchased for the Miami Metrorail.

[13] The first Hitachi cars were delivered in October 2023; the replacement of the rolling stock is set to occur in phases from 2024 to 2026.

[13][14] On February 11, 2018, the MTA announced a month-long closure of the entire system to complete emergency track repairs identified during a safety inspection.