Brown made his Celtic debut in a goalless draw against Kilmarnock on 5 August 2007. Ten days later, he made his UEFA Champions League debut in a 1–1 draw at Spartak Moscow. Brown cleared a header off the Celtic goal line to keep the scores level. His first goal for Celtic came on 25 August, in a 5–0 win against Hearts. Four days later, he played in the return leg against Spartak. Brown won a penalty in extra time, but it was missed by Jan Vennegoor of Hesselink. Celtic went on to win the resulting penalty shootout to qualify for the Champions League group stage. Brown scored in a 5–1 win over St Mirren on 2 September, one week after scoring against Hearts. He played in Celtic's 2–1 win over reigning European champions Milan at Celtic Park.