He signed a two-year deal on 11 May 2007 with the Roar after impressing in the opening rounds of the Gold Coast Premier League with Palm Beach Sharks, leading the goal scoring charts from midfield after 7 matches. Roar manager Frank Farina stated that Nichols was "one for the future" the official press conference following his signing.
Nichols made a solid start to his career in the A-League with a number of substitute appearances. He also received his first call-up to the Australian Under 20 squad for a training camp on 7 October 2007. He scored his first goal for the Roar in his side's 4–1 victory over Perth Glory midway through the 2008–09 season. In the 2011–12 season, the midfielder exceeded expectations pre-season, scoring 10 goals, mostly from long range. He also made the A-league Team of the Season, alongside teammates Thomas Broich and Besart Berisha.
Before he joined Melbourne Victory he went on trial at Danish club Randers. On 13 May 2013, it was announced by Melbourne Victory that Nichols had signed a two-year deal with the club, reuniting him with his former Roar manager Ange Postecoglou. He became Postecoglou’s first new signing ahead of the 2013/14 Hyundai A-League season.
Japanese J1 League Club Cerezo Osaka made multiple bids for Nichols during the January 2014 transfer window, the highest of which reaching $400,000. Melbourne Victory stood firm despite Nichols' interest in the offer, however look set to complete the deal in the hope of acquiring young Australian midfielder, Tom Rogic.
In the end following Nichols' interest in moving and Tom Rogic joining Melbourne Victory, Nichols joined Cerezo Osaka. Nichols made his debut for Cerezo on 11 March 2014, coming off the bench in an AFC Champions League match against Shandong Luneng Taishan, which Cerezo lost 1–3.
On 23 June 2014, Nichols joined Perth Glory on a one-year loan.
On 3 July 2015, Nicholas signed a two-year deal with A-League side Western Sydney Wanderers. Nichols made his Wanderers debut against Brisbane Roar on 8 October 2015, scoring his debut goal for the Wanderers in the 13th minute of the match. On 11 May 2017, it was announced that Wanderers would not be renewing Nichols' contract. On 16 May 2017, Nichols was charged with possession of cocaine and was subsequently banned for four games by the FFA.
Following his charging with possession of cocaine, Nichols dreams to play in Europe were dashed, but Perth Glory signed him on a two-year deal.
Nichols represented the Australia U-20 team during the AFC U-19 Championship in Saudi Arabia. He scored two goals in the Quarter Final match against North Korea including a spectacular overhead kick in extra time. Nichols is currently a member of the Australia U-23 team receiving his first cap in 2010. Nichols made his first senior international debut for the Socceroos on 4 March 2009 in an AFC Asian Cup qualifying match versus Kuwait.As of 20 June 2016
1 – includes A-League final series statistics
2 – includes FIFA Club World Cup statistics; AFC Champions League statistics are included in season commencing after group stages (i.e. ACL and A-League seasons etc.)
Brisbane Roar:A-League Premiership: 2010–2011
A-League Championship: 2010–2011, 2011–12
Australia:AFF U19 Youth Championship: 2008
PFA Team of the Season: 2011–12, 2015–16