According to David Leighton, historian for the Arizona Daily Star newspaper, Sun Tran's history began in 1897 with the organization of the Tucson Street Railway, which by the following year was providing Tucsonans with regular mule-powered streetcar service.

Four years later, TRT published its intent to increase the amount of track for its electric cars but insufficient money prevented this from occurring.

[8] In October 1925, Tucson Rapid Transit Co., having realized that buses were more flexible and economical to run than streetcars and were the future of public transportation in the Old Pueblo, bought the White Star Bus Line.

Also around the same time, Roy Laos Sr., noting the lack of transit service to the south and west sides of town founded the Occidental Bus Line to serve these areas.

After the passage of the Public Utility Holding Company Act of 1935, Federal Light and Traction/Cities Service was forced to sell most of their operations.

Early the following year, the Arizona Corporation Commission decided against OPT and allowed TRT to also provide bus service to the plant.

[12] In 1975, a contest was held to give a new name to the bus system, with Benjamin Rios, a 25-year-old University of Arizona architecture student from Mexico, submitting the winning entry: “Sun Tran.” His prize was a $150 portable television.

[13][6] In summer of 2023, Sun Tran released their Comprehensive Operational Analysis, a pseudo bus network redesign that would increase frequency, realigning and extending routes and improving access and quality of service.

[14] Sun Tran won the America's Best Transit System award for 1988 and 2005 from the American Public Transportation Association in the category of 4 to 30 million annual passenger trips.

Previously, it was $1.75; reduced fare for low-income, persons with disabilities, seniors at least 65 and Medicare cardholders was $0.75 (with a valid SunGO ID & card).

The University of Arizona provided discounted passes for eligible students, faculty and staff through the UA's Parking and Transportation Services.

Copies are available at multiple locations around town, including the Sun Tran offices, many public libraries, community colleges, major malls, pass sales outlets, at other civic facilities around the metropolitan area, and on the buses themselves.

The Sun Tran website also has an online trip planning function, and includes all schedules and maps featured in the Ride Guide.

In May 2006, voters in Tucson approved a Regional Transportation Plan (a comprehensive bus transit/streetcar/roadway improvement program), and its funding via a new 20-year half-cent sales tax increment.

[20] The centerpiece of the Regional Transportation Plan is Sun Link, a 3.9 mi (6.28 km) modern streetcar system (inspired by the successful Portland Streetcar in Oregon) that travels through the downtown area, connecting the main University of Arizona campus with the Mercado District master plan area (known at that time as Rio Nuevo) on the western edge of downtown.

In December 2010, a $63 million federal TIGER grant was awarded to the City of Tucson, meeting most of a remaining funding gap and allowing the modern streetcar project to move forward.

[28] Sun Link is double-tracked, replacing a single-track configuration previously used by Old Pueblo Trolley (OPT), a volunteer-run heritage streetcar operation, begun in 1993, mainly used by tourists and local patrons (including University of Arizona students) of the numerous small shops, bars and restaurants along the line.

Along with this name change comes a new logo and color scheme, replacing the old red, yellow, and white with a blue, yellow, silver, and white livery that extends across not only the Sun Tran buses, but the other services as well (even the renderings and computer animations of the then-under-development Sun Link streetcar were converted to the new design).