He made his Celtic debut, coming on as a 68th-minute substitute, in a 4–2 win against Inverness CT in the third round of the Scottish League Cup on 27 October 2002.

[10] Wallace picked up his first silverware with the club, coming on as a second-half substitute for Stephen Pearson in Celtic's 3–1 win over Dunfermline in the Scottish Cup.

[13] After being sidelined with a hamstring injury, he scored a hat-trick on his return, in an 8–1 rout of Falkirk in a Scottish League Cup tie on 21 September 2004.

[16] However, he made little impact in either his league or European appearances, leading a loan enquiry from Inverness CT, whose bid was rejected.

[19] With the club finished second place in the league and only won the Scottish Cup, Wallace went on to make twenty–one appearances and scoring three times in all competitions.

[12] With the arrival of new manager Gordon Strachan at the start of season 2005–06, Wallace made his first appearance of the season, starting a match against Artmedia Bratislava in the second leg of the UEFA Champions League second qualifying round and set up the second goal of the game for John Hartson before being substituted in the 54th minute, in a 4–0 win that was not enough for Celtic to overcome a 5–0 deficit from the away leg.

[23] Strachan persisted with this team selection for several weeks to the bemusement of fans who could clearly see the player's lack of aptitude for playing in defence.

[3][24] This further highlighted his lack of positional awareness in playing in defence when he scored an own goal in the New Year game against Hearts at Tynecastle, although the club still won 3–2 on 1 January 2006.

[26] But Wallace played in the Scottish League Cup Final at a left back position against Dunfermline Athletic, due to Wilson being cup-tied and Celtic won 3–0.

[35] This was followed up by setting up a goal for Liam Miller, who scored 14 yards past the goalkeeper, in a 3–0 win against Leeds United four days later on 13 September 2006.

[36] However in a match against Ipswich Town on 23 September 2006, he played a role that led Jason de Vos to score an own goal, but was sent–off in the 86th minute for a second bookable offence, in a 3–1 loss.

[37] After serving a one match suspension, Wallace returned to the first team, coming on as a 52nd-minute substitute, in a 4–1 loss against Preston North End on 14 October 2006.

[47] In a follow–up match into the second game away to Birmingham City, Wallace played an integral part in the decisive goal when he provided the free kick that eventually led to Stern John's late equaliser, resulting in a 2–2 draw.

[51] However, it was reported on 18 January 2008 that Wallace had sustained an Anterior Cruciate Ligament knee injury and would therefore miss the rest of the 2007–08 football season.

[56] In the 2008 summer transfer window, it was reported that he rejected a move to Preston North End and stay at Sunderland to fight for his place in the first team.

[57] Following this, Wallace was taken off the transfer listed and he later thanked manager Keane for giving him a second chance to play for the club ahead of the 2008–09 season.

[60] A week later on 23 August 2008, Wallace made his league debut, coming on as a 55th-minute substitute for Barry Nicholson, in a 1–1 draw against Sheffield Wednesday.

[75] However, Wallace was criticised in an interview with The Lancashire Telegraph when he expressed his lack of sympathy on Preston North End's struggles that eventually saw them relegated the following season.

[77] Wallace transferred to fellow Championship club Burnley for an undisclosed fee on 2 July 2010, signing a three-year contract.

[119] He made his first appearance of the season, starting the whole game, in a 1–0 loss against Sheffield Wednesday in the second round of the League Cup on 26 August 2014.

[126] Wallace made his debut for Sheffield Wednesday in the opening game of the season against Bristol City and set up a goal for Lewis McGugan, in a 2–0 loss.

[130] Wallace quickly made an impact since joining the club and was awarded PFA Fans' Players of the Month for August and September.

[134] However in a match against Milton Keynes Dons on 19 April 2016, he received a straight red card after an off the ball incident with Jonny Williams, in a 0–0 draw.

[135] After serving a three match suspension, Wallace returned to the starting line–up against Brighton & Hove Albion in the first leg of the Championshup play–offs and scored in a 2–0 win.

[137] In the Football League Championship play-off final against Hull City, Wallace started and played 64 minutes before being substituted, as Sheffield Wednesday lost 1–0.

[152] In the second leg of the Championship play–offs semi–final against Huddersfield Town, however, he suffered an injury and was substituted in the 5th minute, as the club went on to lose 4–3 on penalties following a 1–1 draw.

[158] However, during a 2–1 loss against Millwall on 20 February 2018, playing in the false nine position, Wallace suffered a knee injury and was substituted in the 79th minute.

[162] Manager Carvalhal responded to Wallace's claims by tweeting on his Twitter account: "Ross did a very good contribution in the first 2 seasons and I must respect this...."[163] Following his release by Sheffield Wednesday, Wallace went on trial at Wigan Athletic and was featured in a friendly match against Tranmere Rovers on 14 July 2018, but failed to win a contract despite impressing the club.

[172] After serving a two match suspension, Wallace returned to the starting line–up against Walsall on 9 March 2019 and played 72 minutes before being substituted, in a 2–0 loss.

[189] Throughout his football career, Wallace made statements that moving to new clubs and performances would benefited his hopes of getting a call–up from the Scotland national team.