Born March 15, 1940 in Pittsburgh, Pennsylvania, Judith Fingeret Krug credited her parents for her aspirations on intellectual freedom and anti-censorship. In a 2002 interview with the Chicago Tribune, Krug told the story of being discovered by her mother as she read a sex education book under her bed covers at age 12. Upon being revealed with what she thought would be an off-limits book, Krug was surprised by her mother's reaction. "She said, 'For God's sake, turn on your bedroom light so you don't hurt your eyes.' And that was that," Krug said.

Krug graduated from the University of Pittsburgh where she studied political theory. She went on to receive her Master's degree in library studies from the University of Chicago. In 1962, Krug worked as a librarian at Chicago's John Crerar Library and later as head cataloger at the Northwestern University Dental School Library. In 1965, she assumed a position as a research analyst for the American Library Association (ALA).

An Advocate for the First Amendment and free expression of ideas, Krug was named director of the American Library Association's Office of Intellectual Freedom upon its founding in 1967. Over the following 40 years of her life, the Pittsburgh native worked tirelessly as an integral part of ALA to protect the public's First Amendment rights including freedom of inquiry, expression, and the privacy to seek out information. In 1969, she became executive director for the Freedom to Read Foundation, which promotes and defends the rights protected by the First Amendment as well as the rights of libraries to provide and include in their collections any and all works within legal standing.

In 1982, Krug founded the renowned Banned Books Week which celebrates the freedom to read and the right of the individual to choose their own reading material. Krug's goal was to ensure that every library should be fully stocked to the standards of the law without fear of government censorship. The unyielding supporter for the freedom to read defended various works from censorship including Huckleberry Finn, The Catcher in the Rye, and Little Black Sambo. Krug, always in support of and advisor to students, teachers, and librarians, was involved in multiple First Amendment cases, some of which went before the United States Supreme Court.

Of Krug's supreme dedication and integrity, friend and children's and young adult author, Judy Blume said the following in 2009: "This is the woman who defended what we wrote, who defended the librarians who selected our books for their collections, and most importantly, who defended the rights of our young readers. For four decades she used her abundant energy and knowledge to protect the Constitutional rights of citizens granted under the First Amendment. She raced around the country speaking out wherever and whenever she was needed. Let's just call her amazing, because she was." Blume's Forever is one of the most commonly banned books.

Since Krug's creation of Banned Books Week, more than one thousand books have been challenged. Books are most often challenged for sexual and violent content as well as the use of profanity or slang, offensive representations of religion or race, and positive depictions of homosexuality. Books challenged range from the classic works of American literature such as The Great Gatsby, to more recent works like Harry Potter; from authors Walt Whitman to William Shakespeare. Krug, however, based her life's work on the battle against government censorship of books, advocating the concept that under the First Amendment, citizens should be able to create their own ideas and freely read those of others.

In a September 1995 issue of American Libraries, Krug said, "If I have an agenda, it is protection of the First Amendment. Libraries in this country cannot operate unless we can stand foursquare on the First Amendment. And if that becomes a partisan position, well, OK, I guess if I have to be partisan I will be partisan on behalf of the First Amendment."

In the last decade of her life, Krug dealt with cases of Internet censorship. In 2002, Krug opposed the Child Online Protection Act that had been passed in 1998 and restricted access to minors of any material concluded harmful. In the Supreme Court case, Krug testified that:

Librarians are concerned about 'quick fixes' that fail to teach young people how to best use the Internet. Internet use policies combined with appropriate education are vital to the well-being of our nation's children. They need to be taught the skills to cope in the virtual world just as they are taught skills to cope in the physical world. Children who are not taught these skills are not only in danger as children in a virtual world, they also will grow into young adults, college students, and an American workforce who are not capable of avoiding online fraud, Internet addictions, and online stalking. Education is our best way to avoid raising a generation of victims.

The Supreme Court found the reason for censoring insufficient in 2002 and as of 2009 the act has remained unconstitutional and unenforced. Another prominent battle Krug faced was the 2003 Children's Internet Protection Act, in which she, with the support of ALA, opposed the act.

Krug received an honorary doctorate, Doctor of Humane Letters, in 2005 from the University of Illinois at Urbana-Champaign. She also received many awards including the Joseph P. Lippincott Award, the Irita Van Doren Award, and the Harry Kalven Freedom of Expression Award. In 2009, Krug became the first person since 1993 to receive the William J. Brennan Jr. Award, which recognized her devotion to the freedom of expression and ideas. In addition to her work in defending intellect, Krug served as senator and vice president of the Phi Beta Kappa society, the nation's oldest academic honor society. She also served on the Chicago chapter of the American Jewish commission board of directors, the Literary Magazines and Presses council, and as the chair of the Media Coalition.

On April 11, 2009, the "Hero of librarians" lost her long battle to stomach cancer at the age of 69. Krug was survived by her husband, Herbert Krug, her son, Steven Krug, her daughter, Michelle Litchman; as well as her sister, two brothers, and five grandchildren.

Of her character, ALA President Jim Rettig released the following statement directly after her death in 2009:

For more than four decades Judith Krug inspired librarians and educated government officials and others about everyone's inviolable right to read. Her leadership in defense of the First Amendment was always principled and unwavering. All who had the privilege to work with her admired her, learned from her example, and enjoyed her sense of humor. Her professional legacy is the thousands of librarians and others who share her commitment to intellectual freedom.