[3] Quincy had been a member of the youth system at hometown club Ajax for nine years when he was released at the age of 16 for alleged attitude problems.

[9] He scored his first goal for the first team in the same competition on 9 November 2004 against Everton, a match in which he also made two assists,[10] and contributed two appearances to Arsenal's victorious 2004–05 FA Cup campaign.

[15] In June 2007, it was reported that Premier League club Birmingham City had expressed interest in Quincy and wanted to bring him back to play in England,[16] but on the final day of the summer 2007 transfer window he joined Spanish side Celta de Vigo on loan for the 2007–08 season with an option to purchase.

[17][18] He made 20 appearances in the Segunda División, of which half were as a substitute, and scored five goals,[19] though he missed several weeks of the season on international duty at the 2008 African Cup of Nations.

[20] He made his debut as a second-half substitute in the first-round League Cup match against Wycombe Wanderers, scoring the fourth goal in a 4–0 win with a fine finish from 18 yards (16 m).

[23] The initial loan was not extended past January 2009, manager Alex McLeish suggesting that financial considerations might have come into play.

[28] Reportedly "available for a small fee", he trained with Championship side Bristol City for ten days in August 2009, but no deal was forthcoming.

[29] On 27 January 2010, Quincy signed for Premier League side Portsmouth on loan for the rest of the 2009–10 season,[30] and made his debut in the defeat at Manchester City four days later, coming on as a late substitute for Hayden Mullins.

[39] After unsuccessful trials at Crystal Palace and Real Valladolid,[40] Quincy signed a one-year contract with Portuguese Primeira Liga club Boavista on 27 August 2014.

[48][49] Quincy appeared at the 2005 FIFA World Youth Championship for the Netherlands national under-21 football team, the Jong Oranje in the summer of 2005.

[50] Though the Netherlands crashed out of the tournament in the quarter-finals after a penalty shoot-out against Nigeria,[51] Described by FIFA.com as "a bit special... full of power, pace and bags of sumptuous skill", Quincy was profiled as one of the Best Players of that FIFA U20 Championship.

[55] Ghana had hoped to persuade him to represent them at the 2006 FIFA World Cup in Germany, but his previous appearances for his native country at youth level precluded that.

[59][60] On 18 December 2007, Quincy was called up by Ghana as part of the 40-man squad[61] for their two-week training camp in Dubai ahead of the 2008 African Cup of Nations.