In a last-minute press conference, the mayor revealed he would be stepping down from his post after serving since 2011.
The upcoming race began to take shape, with potential candidates already throwing their hats into the ring, including former Chicago Police Superintendent Garry McCarthy, who was fired by Emanuel in the wake of the release of video showing the fatal police shooting of Laquan McDonald.
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The mayor's announcement takes place as Officer Jason Van Dyke's trial begins in that case.
Emanuel said he and his wife decided to "write another chapter together" as their three children have left for college.
"[Amy] and I look forward to writing the next chapter in our journey together," an emotional Emanuel said. "I will always be here for the future of this great city. Not as mayor but in the most important role anyone can play. As a citizen."
"From the bottom of my heart, thank you, God bless you and God bless the people of Chicago," he said as he ended his announcement.