On 4 January 2008, Hinkel was confirmed as a Celtic player, for a fee of £1.9 million. Hinkel played his first Celtic game in a 3–0 Scottish Cup win over Stirling Albion eight days later, and scored his first goal for Celtic a month later, in a 3–0 win over Hearts at Celtic Park. Celtic won the SPL title on a dramatic last day of the season and earned Hinkel his first league title medal.
The following season, Hinkel won a Scottish League Cup winners medal after a 2–0 win over Rangers in the final.
Hinkel played a vital part in Celtic’s Champions League third qualifying round second-leg victory over Russian outfit Dinamo Moscow on 5 August 2009. The match ended 2–0 to the Hoops with Hinkel assisting Scott McDonald for the opener then hitting a long hopeful punt up the pitch which Georgios Samaras latched onto before netting a last-minute winner. The German also cleared two goal-bound Dinamo strikes off the line. Hinkel was seen as an inherent and important part of the team and his performances were not put into question, as shown by his 29 SPL matches.