Honolulu Rapid Transit (HRT) was founded on June 6, 1898, the same day that Hawaiʻi was annexed by the United States.

Various issues caused its failure, including a series of strikes by union workers and reports of a hostile takeover of the company by Harry Weinberg in 1955, after he began buying up other properties in Hawaiʻi.

The City & County of Honolulu considered acquiring HRT and its competitors, keeping with the trend as more cities in the United States were taking over operations of privately owned bus companies;[15] the United States Department of Transportation informed Honolulu in August 1970 that it would fund 2⁄3 of the cost to acquire three private lines: HRT, Leeward Bus, and Wahiawa Transport.

[12] On September 14, 1970, and under the guidance of then-Mayor of Honolulu Frank Fasi, the city established Mass Transit Lines (MTL) Limited to oversee operations.

In addition to changing the paint scheme, MTL made the system friendlier by also relaxing the standard uniform, introducing the current short-sleeve shirts featuring TheBus logo, buses, and slogans.

Fasi introduced the "new-identity apparel" in 1974, hoping to change the bus system's stodgy, old image to a fresher, more fun one that would help lure more drivers out of their cars.

[21] By 2006, ridership and profits rebounded thanks to the implementation of programs geared toward college students who commute to school and work, and rising gas prices.

[22] In 2009, ridership for TheBus dipped slightly by 2% due to its July 2009 decision to increase its fares to $2.25, lower gas prices, and a rising unemployment rate.

One major change included the installation of security cameras in its fleet in an effort to deter criminal activity.

"[25]) in the majority of vehicles, and set up a website at hea.thebus.org enabling passengers waiting at stops to track bus locations via cell phone.

[29] Upon tapping a HOLO card to a reader, passengers receive an unlimited number of free transfers for 2.5 hours, including onto Skyline trains.

[33] On December 4, 2013, Mayor Kirk Caldwell announced a plan to place ads on the outside of the buses (but not at stops or in shelters, as these would be prohibited locations per a ban on non-moving outdoor advertising in the state) in an effort to generate money to fund more revenue, restore cut routes, prevent fare increases, and improve the system's infrastructure.

[3][47] TheHandi-Van serves over 3,000 daily riders (with approximately 13,000 eligible total), operates year-round and 24 hours per day, and is the most in-demand paratransit service per capita in the nation.

[47] Due to its low cost and wide coverage, TheBus is a very popular means of travel by high school students.

[31] TheBus has been criticized by local publications such as Honolulu Civil Beat for "heading in the wrong direction", citing both rising fares yet a steady decline in ridership since 2015 despite increasing traffic on the island.

[55] Another fare-free period for all transit on Oʻahu was held to coincide with the launch of Skyline rail service in July 2023.