It is one of six lines on the Metro Rail system, operated by the Los Angeles County Metropolitan Transportation Authority.

Unlike the D Line, these bus routes run along the entire Wilshire corridor, west to Beverly Hills, Westwood, and Santa Monica.

[9] The current D Line is the product of a long-term plan to connect Downtown Los Angeles to central and western portions of the city with a subway system.

Original proposals in the 1980s had the subway line running down Wilshire Boulevard to Fairfax Avenue and then north to the San Fernando Valley.

A 1985 methane explosion at a Ross Dress for Less clothing store near Fairfax gave Rep. Henry Waxman, who represented the Fairfax District, a reason to derail the project that was opposed by his constituents by prohibiting tunneling in an alleged "methane zone" west of Western on Wilshire.

[11] Today's D Line was built in two minimum operating segments: The Hollywood branch (MOS-2B) began service in 1999.

Metro is constructing a major extension of the D line to Mid-Wilshire, Beverly Hills, Century City, and Westwood.

In Beverly Hills, there was public opposition to the D Line Extension, led by school board president Lisa Korbatov.

Korbatov gathered around 5,300 signed petitions to send to President Donald Trump, urging him and Transportation Secretary Elaine Chao to withhold federal funding from the project.

D Line trains pass through Union Station, exit through a portal at Ducommun Street, and stop in the Arts District when they go to and from the Division 20 yard for maintenance and storage.

In 2018, the Metro board approved a $500,000 expense to undertake pre-design activities, prepare an Environmental Impact Report and conduct public engagement for a potential station at 6th Street.