Reno attended public school in Miami-Dade County, Florida, where she was a debating champion and was valedictorian at Coral Gables High School. In 1956 Reno enrolled at Cornell University in Ithaca, New York, where she majored in chemistry, lived in Balch Hall, became president of the Women's Self-Government Association, and earned her room and board.
Reno was named staff director of the Judiciary Committee of the Florida House of Representatives in 1971. She helped revise the Florida court system. In 1973 she accepted a position with the Dade County State's Attorney's Office During this time, questions about Reno's sexual orientation became a major part of Republican opponent Jack Thompson's campaign against her, who demanded to know her sexual orientation. He was repeatedly rebuffed by many critics due to this. She won the race with 69% of the vote. She left the state's attorney's office in 1976 to become a partner in a private law firm.
In 1978, Reno was appointed State Attorney for Dade County (now called Miami-Dade County). She was elected to the Office of State Attorney in November 1978 and was returned to office by the voters four more times. She helped reform the juvenile justice system and pursued delinquent fathers for child support payments and established the Miami Drug Court.
Reno has been criticized for her prosecutions of alleged sexual abusers during this time, which have been described as a "crusade involving the "manipulative questioning" of child witnesses. She was involved in the prosecution of Bobby Fijnje, a 14-year old accused of Satanic ritual abuse who was eventually acquitted.
In 1995, Reno was diagnosed with Parkinson's Disease.
In 1993, Reno was nominated and confirmed as the first female Attorney General under Bill Clinton, after both of his previous nominees, Zoe Baird and Kimba Wood, had confirmation problems when it was revealed both had previously employed illegal immigrants as nannies. Reno remained Attorney General for the rest of Clinton's presidency, making her the longest-serving Attorney General since William Wirt in 1829.
While Clinton could steer a middle ground between his Democratic supporters and the Republican Congress on monetary issues, Reno's job was at the center of a variety of intractable cultural conflicts. This made her a lightning rod for criticism of the Clinton Administration from the right, who often perceived the federal government as a threat to their fundamental freedoms.
After her tenure as attorney general and her unsuccessful gubernatorial election bid, Reno tours the country giving speeches on topics relating to the criminal justice system. For example, on March 31, 2006, she spoke at a criminology conference held at the University of Pennsylvania. At this conference, she stated that she believes that the education system in the USA needs to be improved, as there is a link between the quality of education and the crime rate. She also believes that too much money has been diverted away from the juvenile court system and believes that the government should find some way to make the juvenile courts work effectively so as to prevent problems in troubled children and adolescents before these problems are exacerbated by the time these adolescents reach adulthood.
In 2001, Reno appeared alongside Will Ferrell on Saturday Night Live in the final installment of the recurring sketch "Janet Reno's Dance Party". In another television appearance, on a 2007 Super Bowl XLI TV commercial, Janet Reno was among the guests at Chad Johnson's Super Bowl party.
Reno is also curating a compilation of old-time American songs performed by contemporary artists called the Song of America (album).