Alvarez was the first Hispanic woman elected to this position,[2] after being the first Latina to win the Democratic nomination for state's attorney of Cook County.

Alvarez's successful prosecution of Sykes resulted in his conviction for the predatory criminal sexual assault of a 9-year-old girl who was left paralyzed, blind, without speech and confined to a wheelchair after the brutal attack in the Cabrini Green housing project.

During her first five years in office, Alvarez drafted a law that increased criminal penalties for gang members arrested with guns.

Peter Neufeld, of The Innocence Project says prosecutors rejected the new evidence and suggested necrophilia (having sex with a dead person) as a possible explanation for why a convicted rapist's DNA may have come in contact with the victim, to which Alvarez replied, "It's possible.

[15] In 2010, Tiawanda Moore sought to file a complaint against a police officer for groping her, and secretly recorded an interview with investigators on her smartphone, on the grounds that they were trying to intimidate her.

[17] Judge Stanley Sacks dismissed Drew's case on March 2, 2012, stating the eavesdropping law was unconstitutional and that it was too broad and criminalized innocent behavior.

[19] Judge Sharon Johnson Coleman ruled that the Illinois Eavesdropping Act, 720 ILCS 5/14, violated the First Amendment of the United States Constitution when used as a method to prevent the open recording of law enforcement's audible communications in public places while performing official duties, or the communications of others that are incidentally captured.

[28][29] In the wake of the release of video of the murder of Laquan McDonald, protestors and Chicago politicians called on Alvarez to resign for having waited 13 months to prosecute police officer Jason Van Dyke.

[31] Based on the video, it is believed that at least three of the shots struck McDonald's body as he lay motionless on the ground, conflicting with police reports of the incident.

[31] Another controversial case was a Wicker Park shooting of a homeless man, Sammy Tate, involving two falsely accused black minors.

Alvarez approved the keeping of a 15-year-old minor (Deandre Washington) in solitary confinement in Cook County Jail for 4 years pending trial.

Alvarez also refused to resign when asked, yet settled suit against the city in 2012 for malicious prosecution by local Cochran offices for $1 million.

[33][34] At a 2018 Chicago City Club event, Alvarez's then-press agent still defended the ex-Cook County State's Attorney for not knowing how many minors were kept in solitary confinement during her term in office.

Alvarez was reelected to a second term as Cook County State's Attorney in 2012 after defeating Republican challenger Lori Yokoyama.