From the longer Wikipedia page .
The station was first opened on 1 November 1865 by the North London Railway on its "City Extension" from the North London Line to Broad Street in the City of London. It had three island platforms with four through lines joining the west side of the North London line, and two joining the east. The station had no overall roof. The line to Broad Street and the station closed on 27 June 1986.
Rebuilding the station for the London Overground network began with site clearance in early 2005. The station was opened by the Mayor of London, Boris Johnson, on 27 April 2010.