The station first opened on 7 August 1850 as Colney Hatch station, the Great Northern Railway (GNR) having agreed to provide a station there for the benefit of the Second Middlesex County Asylum being built at Colney Hatch at that time. There were several subsequent name changes: to Southgate and Colney Hatch on 1 February 1855; to New Southgate and Colney Hatch on 1 October 1876; to New Southgate for Colney Hatch on 1 March 1883; to New Southgate and Friern Barnet on 1 May 1923; and finally to New Southgate on 18 March 1971, or, as stated by other sources, on electrification of the line in 1976. The GNR came under the London and North Eastern Railway (LNER) after "Grouping" in 1923, before British Railways took over upon nationalisation in 1948. WAGN operated the service from 1997 to 2006.
In autumn 2008, a new Shere self-service ticket machine, accepting both cash and debit/credit cards, was installed at the eastern street-level entrance here (and similarly at other local First Capital Connect stations), replacing the previous Avantix self-service machine. The PERTIS machine remains in situ.
The typical off-peak service is three trains an hour to Moorgate, reduced to two after 7:00 pm. Night and weekend trains run every 30 minutes. There are three trains an hour to Welwyn Garden City, reduced to two in the late evenings and at weekends.