Superintendent Snelling served nearly three years as the city's top cop and more than 30 years with the Chicago Police Department.
He is highly regarded and well-liked across the city, from peers and community members alike.
Before becoming superintendent, Snelling served as chief of the CPD Bureau of Counterterrorism.
He also served as commander of the 7th District in his native Englewood and has been called a "son of Englewood."
In a statement, Snelling said he's proud of the record-low reduction in shootings, homicides and violent crime in the city during his tenure and he's closing this chapter, "with a heart full of gratitude."
Speaking one-on-one with the I-Team this past December, Snelling described his successful approach to leadership, working across different bureaus.
"It's a combination of this: my philosophy of top-down effect, not bottom-up, that the leadership has to be held accountable, and then the message coming from the top is now spread across the entirety of the city of Chicago with our Chicago police officers, that this is our focus to make sure that we're protecting people in the city, and this is how we do it," Snelling said. "And we train our officers to do it, and make sure that they're following the rules. They're policing constitutionally, which now helps us build trust in the community."
The Community Commission for Public Safety and Accountability will now lead a nationwide search for CPD's next superintendent.
Fred Waller will serve as interim superintendent in the meantime.