Sound Transit extended the T Line by 2.4 miles (3.9 km) to the Stadium District and the Hilltop area west of Downtown Tacoma on September 16, 2023.

Public transit service in Tacoma began with the opening of the city's first horse-drawn streetcar line on May 30, 1888, running on Pacific Avenue between Downtown and Old Town.

[11][12] A second transit plan was proposed without the Federal Way line, which was dropped in favor of express bus service, but retained the Downtown Tacoma connector.

[18][19] A set of 20 potential route alignments were considered for connecting Tacoma Dome Station to the University of Washington campus, the South 13th Street area, and the Theater District.

[20] The preliminary options were narrowed down to five candidates in the draft environmental impact statement, which were grouped based on their use of either Commerce Street or Pacific Avenue to travel north–south through downtown.

[23][24] The Pacific Avenue option was narrowly favored by downtown businesses due to its increased traffic, but Commerce Street was seen as a less controversial route that would allow for easier expansion to the Stadium District.

[27][28] Sound Transit also endorsed studies into making Tacoma Link a fare-free system due to projections that the costs of fare collection would exceed revenue on the line.

[30] Construction of the light rail line near the Tacoma Dome began in August 2000, resulting in a reduction in parking that drew complaints from business owners.

[31] A formal groundbreaking was held on October 18, 2000, shortly after the commencement of Sounder commuter rail service to Tacoma Dome Station.

[32] Work on the downtown section was delayed into the following year due to a contract dispute and design changes to avoid buried telecommunications systems.

[37] The transition between Pacific Avenue and Commerce Street near the future Greater Tacoma Convention and Trade Center was to be via a public plaza, which began construction in June 2001.

[42] Major construction along Pacific Avenue began in February 2002, causing periodic closures that affected buses and businesses who requested the use of mitigation funds to make up for lost revenues.

[43][44] The three streetcars ordered by Sound Transit for Tacoma Link were manufactured in the Czech Republic by Škoda Transportation and delivered in September 2002, costing $3 million each.

[60][61] The project's total cost, $80.4 million, ran above the original estimates due to inflation and additional street improvements, including sidewalks, lighting, benches, and bicycle racks.

[64][65] The study also projected that ridership levels would require a new fleet of two-car trains and longer platforms for the rest of the line, leading to increased costs.

[77] The Hilltop Extension was approved by voters as part of the Sound Transit 2 ballot measure in 2008 and was estimated to cost $217 million, primarily paid for by local funding and federal grants.

[86][87] Sound Transit attributed some of the delay to incorrect city records on the location of utility lines as well as change orders for catenary pole installation.

Outbound trains travel west from an operations and maintenance facility located on East 25th Street near McKinley Avenue to the line's terminus at Tacoma Dome Station.

[96] T Line trains then turn north onto Pacific Avenue and travel in the median for several blocks parallel to Interstate 705, splitting into two tracks after South 21st Street.

[57][99] On Commerce Street, Link trains share lanes with mixed traffic through a major bus transfer area for Pierce Transit.

[89] The T Line passes Wright Park and turns south onto Martin Luther King Jr. Way with two stops in the Tacoma General Hospital complex.

[77][89] The six original stations on the T Line are built with 90-foot (27 m) platforms that are long enough to accommodate one car at a time, but were designed to support further expansion for multi-car trains.

[17] A restoration of 10-minute frequencies was planned as part of the Hilltop Extension's opening in 2023, but was reduced to 12 minutes due to operational issues and a lack of break time for drivers.

[112] Fares were originally not charged on the T Line, with operating costs covered by Sound Transit and $29,000 annually from the Tacoma Business Improvement Area.

[119] The proposed fare was unpopular with riders, business owners, and local boosters due to the potential impact on tourism, with a predicted 25 percent drop in ridership.

[122][123] The Tacoma Business Improvement Area agreed to renew its $29,000 annual subsidy in April 2016, covering the equivalent of a $2 fare until the opening of the Hilltop Extension.

[128] All streetcars in the T Line fleet are stored and maintained at an operating base located east of Tacoma Dome Station and Freighthouse Square.