On 28 January 2011, despite interest from Rangers, Commons signed a three-and-a-half-year deal with Celtic for a fee of around £300,000 and was given squad number 15. The following day, he made an immediate impact, scoring the opening goal on his debut in Celtic's 4–1 League Cup semi-final win against Aberdeen with a lob from outside the box. On 6 February, Commons scored against Rangers in a Scottish Cup tie at Ibrox. The match ended 2–2. On his home debut at Celtic Park, he again scored against Rangers to add Celtic's third goal. In his next home league game, Commons scored both goals, including a volley from 25 yards, as Celtic won 2–0 against Hamilton. Commons had now become an integral part of the Celtic side; playing just behind the main strikers, occasionally in a central role but more often fielded wide left.
Commons began 2011–12 season as a regular in the Celtic team, but in their fourth league match of the season against St Johnstone, he missed an early penalty after slipping at the vital moment. Celtic ended up losing 0–1. As a result of missing the penalty, Manager Neil Lennon removed Commons as a penalty taker. On 2 October 2011, in the second half of Celtic's 2–0 defeat against Hearts, Commons was shown a straight red card for a dangerous tackle. Commons was struggling to match the form he had shown the previous season and, also hampered by suspension and injuries, was no longer playing regularly. On 29 April 2012, Commons scored his first, and only, goal of the season in a 3–0 win over Rangers on 29 April 2012. Celtic finished the season as league champions, and Commons' 24 league appearances saw him gain an SPL winner's medal.
Commons withdrew from the Scotland squad for the 2011 Nations Cup matches in May 2011, claiming that he was exhausted at the end of the 2010–11 season. Injuries and loss of form meant that he was not selected during the 2011–12 season by Scotland manager Craig Levein. Despite Commons showing improved form early in the 2012–13 season, Levein claimed that he would not pick Commons because he had seven alternative players available.