Route 42 commenced operation on 25 July 1912 as a daily route between Finsbury Park station and Clapton Pond via Seven Sisters Road, Amhurst Park and Upper Clapton Road.

On 26 August 1912, it was extended from Clapton to Tower of London via Hackney, Whitechapel Road, Aldgate and Minories.

[1] The route was reduced from a daily allocation of eight vehicles at the beginning of 1970 to only three by 1985, when the evening service was also withdrawn.

[2] Route 42 was included in the sale of Limebourne Buses to Connex in July 2001.

On 3 October 2009, East Thames Buses was sold to Go-Ahead London, which included a five-year contract to operate route 42.