The move was announced on Zenit's official website on Wednesday, and the Russian club confirmed the Serbia international has signed a two-and-a-half year contract.
Here is Ivanovic with his new jersey, per the Zenit Twitter account:
The Blues posted the following on social media, paying tribute to their former defender:
Chelsea manager Antonio Conte's transition to a three-man defence took its toll on Ivanovic after the veteran fell further from the Italian's first-team plans, with other figures preferred in his 3-4-3 system.
Prior to Wednesday's announcement, Conte confirmed Ivanovic's desire for more first-team football was fuelling his departure, and the Blues boss suggested it was the player's decision to leave, per Sky Sports:
Honestly, I didn't speak with the player about this decision. For sure we know is talking with other clubs but until now I don't know anything. We have to wait.
He has played a lot of games for Chelsea and has won a lot here. He is 32 years old and can play many more years at the top level but it's important to respect the player's decision.
If you are not playing a lot, you can make a decision to go to another team but, with respect for him, I am sorry to see him go. When you start the season with a certain group and you try to create a link between the staff and players, we are sorry if someone decides to go away.
However, the 32-year-old could still prove to be a major asset under the right conditions, and Zenit manager Mircea Lucescu will hope he can offer the right setting for his new arrival to excel once again.
Ivanovic leaves Stamford Bridge with a glittering silverware stack, having won the UEFA Champions League, two Premier League titles, three FA Cups, a UEFA Europa League crown and more during his stay.
Here's a look at just how successful he was during his time at Chelsea:
It's that kind of mentality Zenit will be hoping to see more of as Ivanovic settles into his new surroundings, looking to bring a winning attitude with him as he hopes to add to his trophy collection.