He lost to Michael Portillo in the selection for the 1984 Enfield Southgate by-election, but was later selected for Hendon South in the London Borough of Barnet and was elected as the Member of Parliament for that seat at the 1987 general election. He served as PPS to Tony Newton, when Newton was Leader of the House of Commons. After the 1992 general election, the Boundary Commission recommended that the four Barnet seats be reduced to three. Sir Sydney Chapman was retained as the candidate for the Chipping Barnet seat, the only one not being abolished, and John Gorst, the sitting MP for Hendon North, was selected to contest the new Hendon constituency. Marshall was therefore pitched together with Hartley Booth, the MP for Finchley, in trying to win the nomination for the new seat of Finchley and Golders Green. Both MPs put a great deal of effort into the fight, hiring minibuses to ensure all their supporters got to the selection meeting; the contest became bitter when Booth accused Marshall of "signing up the dead and the dying" as Conservative members in order to boost his chances of victory. The new Finchley seat, not too dissimilar to the old Finchley seat, was thought to become a Tory seat, even if marginally held; when Mrs Thatcher held the old seat she had majorities of nearly 10,000. Despite most of the new constituency coming from Booth's old seat, Marshall won the selection contest on 1 November 1995, but went on to lose the contest for the seat to the Labour Party candidate Rudi Vis at the 1997 general election; where the Conservatives experienced their worst electoral defeat in 91 years. Notable losses included Michael Portillo, who Marshall himself lost to in the Conservative selection for the Enfield Southgate by-election thirteen years earlier, along with Cabinet Ministers: Michael Forsyth, Malcolm Rifkind, Ian Lang, William Waldegrave, Roger Freeman and Tony Newton. As well as many high-profile Conservative figures losing their seats, the party lost all their representation in Scotland & Wales, making them an England-only party.
After Parliament
In May 1998 Marshall was elected to Barnet London Borough Council for a ward in his old constituency and following the Conservative victory in local elections in 2002, he has served in the Cabinet. He unsuccessfully sought to regain his Finchley and Golders Green seat at the 2001 general election, but Vis beat him by 3,716 votes. Among other roles, Marshall served as Cabinet Member for Investment in Learning, responsible for implementing the Primary Schools rebuilding programme, and the Libraries Strategy, which modernised library provision across the Borough. He was an unsuccessful candidate for the leadership of the Conservative group in 2005. John Marshall was Mayor of the London Borough of Barnet in the Municipal year 2008–2009.
