Van Dyke appeared emotionless as the verdict was read and he was remanded into custody.
WATCH: Verdict read in Jason Van Dyke trial
The verdict is the latest chapter in a story that has led to the police superintendent and the county's top prosecutor both losing their jobs - one fired by the mayor and the other ousted by voters. It also led to a U.S. Justice Department investigation that found a "pervasive cover-up culture" and prompted plans for far-reaching police reforms. Three officers have been accused of conspiring to cover up what happened that night to protect Van Dyke.
Van Dyke, 40, was the first Chicago officer to be charged with murder for an on-duty shooting in more than 50 years.
WATCH: Jason Van Dyke taken into custody
Outside Chicago City Hall, dozens of demonstrators gathered and cheers erupted Friday afternoon. Marchers took to the streets of downtown Chicago in celebration of the verdict, closing streets. Thousands of Loop workers were told to leave their offices following the announcement that a verdict would be read, packing trains out of downtown during midday.
Demonstrators shut down Chicago streets
"We're not done!" and "This is just the beginning!" Frank Chapman told the crowd with a megaphone.
The group continued to rip the mayor and city politicians, who they say purposely withheld the Laquan McDonald dashcam video released in November of 2015, the same day Van Dyke was charged and more than a year after the teen was killed.
Laquan McDonald, Stephon Clark and other police shooting deaths that shocked the nation
Another protester warned politicians, "we are going to take your seats," referencing a "black wave" coming.
Van Dyke was charged with first-degree murder, 16 counts of aggravated battery with a firearm - one for each shot - and official police misconduct in the October 2014 shooting.
RELATED: What's next for Jason Van Dyke?
The end of the trial represented closure for McDonald's family, who said the focus should now be on healing and creating positive change.
"The verdict of that jury today represented the committal and benediction for us," said Rev. Marvin Hunter, McDonald's great uncle, who spoke on behalf of the family. "Now we can go home tonight and sleep knowing that Laquan is at peace and knowing that the people that harmed him unjustly will face whatever they have to face."
Still, Hunter, who looked over to Van Dyke's family after the verdict was read, said the outcome was still bittersweet.
"I could see the pain in those people and it was touching my heart to see their pain," he said.
What's the difference between first-degree and second-degree murder?
First-degree murder carries a sentence of 20 years to life. The jury was able to consider second-degree murder, a sentence which varies widely from probation up to 20 years. Second-degree murder is considered to be a first-degree murder with a mitigating factor, the judge explained before the foreman read the jury's verdict.
First-degree murder requires a finding that the shooting was unnecessary and unreasonable. The judge told jurors the second-degree charge required them to find Van Dyke believed his life was in danger, but that the belief was unreasonable.
Aggravated battery with a firearm carries a sentence of six to 30 years per charge.
"We considered the mitigating factor of how he perceived his actions, of the imminent and the escalating risk, and why he took that action. But we did decide that taking the action was unreasonable. But we did consider what he thought when he was taking that action," one juror said.
Jason Van Dyke trial jurors: 'We didn't come here for race. We came here for right and wrong'
Laquan McDonald Shooting, Dashcam Video
Police encountered McDonald on Oct. 20, 2014, after a 911 call reported someone breaking into vehicles. As Van Dyke arrived, police had the 17-year-old mostly surrounded on a city street. An officer with a Taser was just 25 seconds away.
TIMELINE: Laquan McDonald Shooting, Jason Van Dyke Case
Van Dyke claimed he opened fire on the teen, who was holding a small knife, because he feared for his life and continued to fire after McDonald was on the ground because he believed he was still a threat.
Prosecutors have argued that each shot was a crime and robbed McDonald of the chance of survival.
WATCH: Prosecution makes closing arguments, rebuttal closing arguments
Prosecutor Jody Gleason seized on the testimony of one the defense's own witnesses, a psychologist who interviewed Van Dyke.
Dr. Laurence Miller said that when Van Dyke heard on his radio that McDonald had a knife and had punctured the tire of a squad car, he told his partner: "Oh my God, we're going to have to shoot the guy."
Gleason said Van Dyke had made up his mind about what he'd do before even arriving at the scene.
"Laquan McDonald was never going to walk home that night," she said.
Gleason pointed to the dashcam video, which showed Van Dyke shooting McDonald 16 times as the teen held the knife at his side. She noted that Van Dyke told detectives that McDonald raised the knife, that Van Dyke backpedaled, and that McDonald tried to get up off the ground after being shot.
Gleason told jurors that while police officers are allowed to use deadly force in some circumstances, this was not one of them.
"They do not have the right to use deadly force just because you will not bow to their authority," she said. "This is not the Wild West out here ... where an officer can shoot an individual ... and try to justify it later."
WATCH: Defense makes closing arguments
Van Dyke's attorney, Dan Herbert, said the dashcam video, the centerpiece of the prosecutor's case, doesn't tell the whole story and is "essentially meaningless based on the testimony" jurors heard.
He pointed to testimony from Van Dyke's partner that night, Joseph Walsh, who said he saw McDonald raise the knife, even though the video doesn't show that. Van Dyke made similar claims on the witness stand as he told jurors that he was afraid for his life and acted according to his training.
"The video is not enough," Herbert said. "It shows a perspective, but it's the wrong perspective."
When asked which way they were leaning, one alternate said, "I would say guilty. He should have waited longer. I mean, he knew the Taser was coming. That's what did it for me."
"Where was he actually causing an issue that, you know, Jason Van Dyke thought that he needed to use deadly force?" the other alternate juror said. "I just don't understand that."
Among the reactions issued Friday following the verdict, Chicago Mayor Rahm Emanuel and Police Supt. Eddie Johnson released a joint statement saying:
For the past several weeks, a jury heard testimony, weighed evidence and considered the facts of the Van Dyke case. Today, the jury reached its verdict. As we absorb their decision, let us continue to hear each other and partner with each other - as public servants, police and members of the public - and let us ensure our collective mission is what endures for generations to come. We come from many neighborhoods, many walks of life and many places throughout the world. But for all of us, this is our home. This is the city we love. We have heard that message countless times in recent days and weeks in church basements, in community meetings and from residents in our neighborhoods. And while the jury has heard the case and reached their conclusion, our collective work is not done. The effort to drive lasting reform and rebuild bonds of trust between residents and police must carry on with vigor.
Jason Van Dyke Trial
Before the verdict, the judge asked everyone in the courtroom to maintain composure, and asked those who felt they couldn't react reasonably, to leave. A woman in the Laquan McDonald family group got up and left the room prior to the reading.
On Friday morning, the jury sent the court a note asking on the aggravated battery charges whether to consider the order of the shots or just the total number of shots.
During the trial, the medical examiner testified that she could not determine the order of shots in the autopsy findings, but showed the jury each bullet wound from head to toe, and what effect it had on Laquan McDonald as he died.
The judge instructed jurors to only consider the simple number of shots fired.
LIVE BLOG: Jason Van Dyke trial on Laquan McDonald murder charges
The jury, which deliberated for about seven hours total on Thursday and Friday, was comprised of eight men and four women. Seven are white, three are Hispanic, one is Asian-American and one is African-American.
One of the last images prosecutors showed jurors was an autopsy photo of McDonald's body. Gleason noted bullet entry and exit holes.
"Laquan's body was riddled, broken and bleeding," Gleason said. "He even had bullet fragments in his teeth."
Herbert argued that McDonald was to blame for what happened that night, saying "the tragedy ... could have been prevented by one simple step."
Herbert then dramatically took the knife that was entered into evidence earlier and dropped it on the floor in front of the jury box.
Herbert also reminded jurors that a prosecutor briefly mentioned the issue of race during opening statements but never broached the issue again.
"Did you see any evidence that race had anything to do with this case?" he said. "When you don't have evidence, you use argument."
As jurors began deliberating, the Chicago Police Department canceled days off and put officers on 12-hour shifts. An extra 4,000 officers will be on the street, according to spokesman Anthony Guglielmi. The city saw protests after video of the shooting was released. Massive protests were expected around City Hall in Chicago's Loop after the verdict was read.
Hunter acknowledged the attention his family's case has gotten and had a message for those that want to continue the momentum created by the verdict.
"America was on trial here, and people all over America and all over the world have been waiting to see what was going to happen. ... Laquan represents all of the victims that suffered what he suffered across the country," he said. "We must go back to our wards, we must go back to our counties and we must begin to become a part of the political process. We must exercise our civic duty properly."