[5] He began his career in London as a trainee with Queens Park Rangers in August 1995, making his League debut in a 2–1 defeat against Manchester United at Old Trafford on 30 December.
[10][12] By July, he reportedly had attracted interest from several clubs, including West Bromwich Albion and Birmingham City with Portsmouth understood to have made an offer.
[12] He quickly established himself in the first team, making 37 league and cup appearances in the 2001–02 season as Portsmouth finished in the lower half of the First Division.
[14][15] He made a further 44 appearances in the 2002–03 season[16] and was club vice-captain[citation needed] when Portsmouth won the First Division championship and were promoted to the Premier League.
The chairman of Southampton, Rupert Lowe, said, "Harry really wanted Nigel – he thinks he is a strong character who will add to the dressing room.
"[22] A training ground injury prevented Quashie from making his debut against Liverpool on 22 January 2005[24] and he did not appear until the match against Everton on 6 February.
[27] However, following Redknapp's departure and his replacement with George Burley,[citation needed] Quashie was allowed to leave Southampton in the January 2006 transfer window.
He was allowed to leave in the January 2007 transfer window as he expressed a wish to return to the Premier League and manager Tony Mowbray wanted to raise some revenue to bring in new players.
[33] Quashie made his debut against Fulham a few days later[34] and went on to make eight appearances, none of them on the winning side,[32] as West Ham battled against relegation.
[35] The signing of Swiss international Valon Behrami in the summer of 2008 and the emergence of academy graduates Jack Collison and Junior Stanislas meant that competition for midfield places was much stiffer,[citation needed] and Quashie spent much of the next 18 months out on loan.
[42] He made three appearances for the team[43] and was praised by manager Mick McCarthy for his leadership before quickly dropping out of contention as the club won promotion to the Premier League as champions.
[47] He made a losing start to his MK Dons career, coming on in the first half for Luke Howell in the 4–3 home defeat to Carlisle United on 24 November.
[43][51] On 13 April 2012, Quashie joined 1. deild karla club Íþróttafélag Reykjavíkur on a two-year contract as both a player and as assistant manager to Andri Marteinsson.
[53] Following the dismissal of Andri Marteinsson on 21 August with ÍR at the bottom of the division, Quashie was appointed to take charge of the team until the end of the season.
[58] He was a member of several England under-21 squads during the 1996–97 season before making his debut at that level on 30 May 1997 in the starting eleven for a European championship qualifier against Poland in Chorzów.
Quashie scored on his second appearance three days later, side footing home in the 34th minute to put his team 4-0 ahead v Trinidad and Tobago at Easter Road, Edinburgh.