Southgate station opened on 13 March 1933 with Oakwood on the second phase of the northern extension of the Piccadilly line from Finsbury Park to Cockfosters. Prior to the station's opening, alternative names were suggested including "Chase Side" and "Southgate Central". On opening, local residents were given a free return ticket to Piccadilly Circus.
The station is built in the Art Deco/Streamline Moderne design style using brick, reinforced concrete and glass and is one of the best known of the many stations Charles Holden designed for London Underground. The station building is circular with a flat projecting concrete roof. Externally, the flat roof of the raised central section appears, impossibly, to be supported by nothing more than a horizontal band of windows that provide daylight to the ticket hall. The roof is actually supported, umbrella-like, from a central column within the ticket hall. The whole building is topped by an illuminated feature resembling a Tesla coil.
Like Arnos Grove, Oakwood and Cockfosters, Southgate is a listed building in this case at Grade II* (regraded from Grade 2 in 2009) and retains much of its original decoration. The two escalators have the original column lighting, while bronze panelling is in evidence throughout the station. However; the station is not without change: in the late 1990s, one of the three entrances was filled in to be used as a new ticket office, and due to the design of the automatic barriers, one of the two remaining entrances is exit only.
In 2008 the station was extensively renovated, with new tiling at platform level, a partial new floor in the main ticket hall, and improved signage throughout.. The station won the London Regional category award at the 2008 National Railway Heritage Awards for the modernisation of a heritage station.
The preserved condition of the station's original features, particularly the escalators, makes Southgate popular for filming scenes for period dramas, including scenes for the 1999 version of the film, The End of the Affair.
The station was developed as a bus/underground interchange and the main building sits on an island between Southgate Circus and Station Parade where a series of bus stops are located. A secondary building containing shops wraps around the other side of the parade.
The station is located on a hill and whereas the platforms at the stations on each side are on the surface those at Southgate are in a short section of tunnel. The tunnel portals are visible from the platforms when looking north, a unique occurrence for a deep-level London Underground station. As usual on the Piccadilly Line, the platforms are labelled Westbound and Eastbound. However, the tunnels run roughly north-south at Southgate, so eastbound is northbound and westbound is southbound.
In the early 1980s, moving picture advertising was tested in the tunnels south of the station. The pictures were of a child on a beach turning to face the camera.
Southgate is the northernmost below ground station on the London Underground network.