Citybus was established on 5th August 1977 by Lyndon Rees, a former China Motor Bus employee. Initially it operated a single Volvo B55 double decker, providing a shuttle service for Hong Kong United Dockyard in Hung Hom. From then it expanded into operating staff and residents' services, including one from City One Shatin to Kowloon Tong MTR station in 1982.
In 1984 Citybus started operating a cross-boundary bus service between Hong Kong and Shenzhen. In 1985 Citybus introduced 5 air-conditioned Leyland Olympians. After the purchase of Citybus by CNT Group in the late 1980s, Citybus began operating several residents' services linking housing estates to MTR stations, using 100 new Olympians.
1991 was the year the Citybus first entered the franchised bus scene, when it was awarded the franchise to operate Hong Kong Island Route 12A (Admiralty [Tamar Street] to Macdonnell Road). This franchise had initially been operated by China Motor Bus, at the time the bus company operating the Hong Kong Island bus franchise.
In September 1993, Citybus won a competitive tender to operate a further 26 Hong Kong Island franchised bus routes, also formerly operated by China Motor Bus. These 26 routes Citybus branded as "Network 26". To operate these routes, 101 non-A/C Leyland Atlanteans were purchased from Singapore's Singapore Bus Services.
In 1995 a further 14 franchised routes were given to Citybus, again, formerly operated by China Motor Bus. At this time the fleet had been expanded to more than 500 buses. During the next few years, Citybus increased its penetration of Hong Kong Island, pushing nearly all of China Motor Bus' remaining routes into low profitability.
In 1996 Citybus was granted a tender to operate 13 routes serving the new airport at Chek Lap Kok, and the new town of Tung Chung. With the opening of the new airport in 1998, Citybus set up the 'Cityflyer' service, which operates (at that time) 5, now 6, airport express routes with the prefix 'A'.
In 1998 the remaining franchise held by China Motor Bus expired and was not renewed. A further 12 routes were therefore transferred to Citybus, and the rest of the franchise was given to a new operator, New World First Bus.
In 1999 Citybus was purchased by Scotland's Stagecoach Group, and the 2001 the cross-boundary bus service was terminated.
Then in 2003 Citybus was bought by Chow Tai Fook Enterprises, which also owns New World First Bus. After a series of restructurings, Citybus and New World First Bus both became subsidiaries of NWS Transport Services Limited, a company jointly owned by Chow Tai Fook Enterprises and NWS Holdings Limited. Both Hong Kong Island franchised bus operators thus became jointly operated, and began to share infrastructure, services and resources, although they retain separate corporate identities.