Many people are saying the McDonald case was Alvarez's undoing. The Chicago teen was shot 16 times in October 2014 by a Chicago police officer.
The shooting was recorded on dash-cam video. The release of that video in November 2015 sparked massive protests in Chicago that gained national attention.
It took Alvarez more than a year to charge Officer Jason Van Dyke in McDonald's murder.
Voters decided Tuesday that was just too long, ousting Alvarez and electing Foxx as their Democratic candidate in the race for Cook County's top prosecutor.
"I have been criticized that I wasn't a very good politician. That's probably right. That's why I stand before you tonight. But I am very damn proud of the fact that I am a good prosecutor. I have been," Alvarez said Tuesday night.
Alvarez said she called Foxx to assure her of a smooth transition and thanked her supporters.
"Obviously, we hoped the results would have been different. But I just want to say I'm proud to stand up here as your state's attorney and I'm very, very proud of the work that I have done in this job. So thank you, thank you," Alvarez said.
Foxx, former chief aide to Cook County Board President Toni Preckwinkle, will take on Republican Christopher Pfannkuche in November.
Pfannkuche is currently in private practice as an attorney, but was with the State's Attorney's office for 31 years. He has said recent he doesn't like what he's seeing.
"I got angry at the way the office was morphing into something that it wasn't under Anita Alvarez," he said.
Many shared the outrage at how Alvarrez handled the Laquan McDonald case. Activists who organized protests and a voter drive call their campaign victorious, but see more work to do.
"Kim Foxx did not win this campaign, Anita Alvarez lost this campaign because we pushed this city to see what Anita Alvarez has been doing to this city and its people," said Tess Raser of Assata's Daughters, an activist organization.
"A part of this work is as much about telling politicians, 'If you don't love black people we are going to fire you,' as well as telling young black people it's up to us, we are the ones we have been waiting for, we are the ones who are going to save us," said Page May of Assata's Daughters.
Those who organized the #ByeAnita campaign say they didn't endorse any particular candidate. They want to see systemic change and whoever becomes the lead prosecutor for Cook County will be under the same scrutiny and subject to the same protests and campaigns if they do not see the systemic change they are hoping for.
Foxx spoke with ABC7 Eyewitness News on Wednesday morning.
Foxx said she plans to evaluate what the needs of the office are and put together a transition team to tackle the struggles the office is facing, should she win the election in November.
"I think we have an issue of violence here in Cook County that is plaguing neighborhood where children aren't safe to go outside and play. So we need to really be mindful and strategic about how to deal with gun violence in a meaningful and strategic way," Foxx said.
Foxx also said restoring credibility in Cook County's criminal justice system - bridging the divide between the community and law enforcement, is top of mind.
"My oath as the state's attorney is to uphold justice on behalf of the people of Illinois, particularly in Cook County. My reassurance is that I take that oath very seriously. I ran for this office to make sure that we had a criminal justice system people can believe in. That's my duty," Foxx said.
At Millennium Station Wednesday morning, Foxx thanked her supporters and spoke on her plans for change.
"I'm very excited about this next chapter. I'm very excited about going into the general election and tackling the big issues facing Cook County," Foxx said.