Ivanovic's contract at Stamford Bridge was set to at the finish of the season, but opted out to earn playing time as it's all footballers' dream.
Branislav Ivanovic, a Serbian international, joined the English Premier League side in January 2008 and went on to make about 400 appearances at Stamford Bridge and won two Premier League titles as well as the Champions League.
"I can say I'm very happy to come here, and to be at a big club like Zenit, I hope together we'll have success," he told the club's official website after they had announced the deal.
"I had a very big hope to come back to Russia and to play here. I am motivated and I think that I can play for many more seasons at the top level.
"I can say that I am excited to be here and everything went smoothly.
"I am happy just to play. I am happy in the centre or on the right. That's probably a question for the manager but I am happy to play in any position."