Running between Chalk Farm and Hammersmith Grove, it is operated by Transport UK London Bus.

[1] The route operated through World War II, when it was used by famous passengers including Peter Cushing to reach the Q Theatre near Kew Bridge.

[5] London United commenced a further contract on 10 November 2012 with the route extended from Turnham Green to Chiswick Business Park.

[6] The extension was funded by the London Borough of Hounslow through developer contributions from Chiswick Business Park.

Abellio London was awarded the contract for route 27 when it was re-tendered effective 9 November 2019 from its Battersea garage.