The undercover officer witnessed someone shoot and kill a 26-year-old man near the 4000-block of West Madison Street in the West Garfield Park neighborhood, police said.
The officer started to follow that suspect, who was in a white pick-up truck. When the driver realized he was being followed, he got out of the pickup truck, pointed a gun at the police officer's vehicle, and fired multiple rounds.
The officer was hit in the wrist and while in route to the hospital, the injured officer spotted the pick-up truck and insisted the pursuit continue.
"The officers driving the transporting vehicle asked the injured officer, who at this point had been shot, did he still want to go directly to the hospital or should they apprehend the offender," Interim Chicago Police Superintendent Charlie Beck said. "He elected that they should apprehend the offender."
The suspect's vehicle crashed in the 2000-block West Congress Parkway and police took two suspects into custody.
The 26-year-old man shot on the street was pronounced dead at Stroger Hospital.
The injured officer, who has been with the department for more than 20 years and is in his 40s, is expected to make a full recovery.
Police said he was not in the area of the fatal shooting as part of an undercover operation; he just happened to be there when it occurred.
Chicago Mayor Lori Lightfoot thanked responding officers during the Wednesday press conference.
"There is no question that the officers' work today in recognizing the danger that the community was in, from the offender who was fleeing the scene, ended up saving other lives," Lightfoot said. "We owe him and the rest of the team a debt of gratitude."
A police investigation into the shooting is underway.