Early years DeMange was raised in the
Ballygall area of
Northside Dublin. He first showed his potential as a schoolboy footballer, playing for St Kevins CBS,
Stella Maris and
Tolka Rovers before moving on to
Home Farm where his teammates included
Brian Mooney. Made his
League of Ireland debut for Farm at
Athlone Town on 8 November 1981. While playing for Home Farm, he was awarded the Young Player of the Year title for the 1982–83 season by the
Professional Footballers Association of Ireland He also finished as the team's top goalscorer with seven goals.
Liverpool In August 1983 DeMange, along with
Brian Mooney, signed for
Liverpool but in four seasons with the club, he never made a competitive first team appearance. He did however help
Liverpool Reserves win two consecutive
Central League titles in 1984 and 1985. During the 1984–85 season he was top scorer for the Reserves, scoring 12 goals in 32 league appearances. In December 1986 he also had a successful loan spell with
Scunthorpe United, scoring 2 goals in 3 leagues appearances. He also played for Scunthorpe in 1
FA Cup game and scored 1 further goal. In May 1987, while still playing for Liverpool Reserves, he made his international debut for the
Republic of Ireland.
Leeds United In September 1987 DeMange was sold to
Leeds United for a fee of £75,000. He subsequently scored on his debut for United, with a diving header, in a 2–0 win against
Manchester City at
Elland Road on 26 September 1987. However this was also the only goal he scored for the club. In his brief spell with United, DeMange went on to make 20 first team appearances, 15 of them in the league.
Hull City In March 1988 DeMange was sold to
Hull City for a fee of £65,000. He subsequently made 68 league appearances and scored 1 league goal for City. He also made a further 4 appearances for City in the
FA Cup and 1 in the
League Cup. In October 1988 he also won his second senior international cap while at City. In November 1990 and in March 1991 during loan spells with
Cardiff City, he also made a further 15 league appearances.
Return to Ireland After leaving
Hull City in June 1992, DeMange returned to Ireland where he played for several clubs in both the
League of Ireland and the
Irish League. Playing for Limerick in the 1992-93 season, he helped the club with the League Cup. During the 1994–95 season he played for a
Dundalk team managed by
Dermot Keely and he helped the club win the League of Ireland title. During the campaign he scored 3 league goals, 2 against
Monaghan United on 11 November 1994 in a 4–0 away win and 1 against
Cobh Ramblers on 12 December 1994 in a 2–2 away draw. ==International career==