McGeady seals Spartak switch
"Today we completed the signing of Aiden McGeady who joined our club on a long-term contract," Spartak said on their website on Friday.
Spartak did not disclose the financial details but both Russian and British media reported the fee for the 24-year-old winger was around 9.5 million pounds.
After putting pen-to-paper, McGeady paid tribute to Celtic and the club's fans.
"The Celtic fans are second to none and it is a fantastic club to play for," he said on Celtic website.
"Celtic is the team I have supported my whole life and will miss so many things, however I am looking forward to the challenge of playing for Spartak Moscow."
The signing comes after prolonged negotiations between the two clubs that took nearly two months to complete.
Spartak hope McGeady will have an immediate impact, helping them revive their stuttering domestic season as well as play a big role in the upcoming Champions League campaign.
Spartak, the most successful Russian club with nine league titles since 1992, are in eighth place, trailing league leaders Zenit St Petersburg by 19 points midway through the season.