To Kill A Mockingbird: The life and afterlife of Harper Lee's misunderstood classic

Ask anyone which American novels they read at school, and Harper Lee's To Kill a Mockingbird (1960) will almost certainly feature. One of the most commercially, critically and pedagogically successful works of all time, this novel about a lawyer's family in the 1930s Deep South won the 1961 Pulitzer Prize, has sold more than 30 million copies, and featured on the majority of reading lists ever since. British librarians called it a book "every adult should read before they die", while Publishing Triangle listed it as one of the 100 best lesbian and gay novels (as a lesbian "coming-of-age" tale). A special edition (Arrow, £6.99) has been published to mark, in the blurb's words, "the fiftieth anniversary of this unforgettable classic".

Regarded as suitable for the young reader – for its young girl's first-person narrative voice, albeit from an adult distance, and for its educative tone – it has been widely adopted as a set text. The film (1962), produced by Alan J Pakula and directed by Robert Mulligan, is best remembered for Gregory Peck's Oscar-winning performance as Atticus Finch. It is 25th on the American Film Institute's list of best American movies, with Atticus named in 2003 as the greatest movie hero of the 20th century.

Indeed, the figure of Finch has been held up by the legal profession and teachers alike as a modern prophet, a Christ-like fount of goodness and wisdom – "the Abe Lincoln of Alabama". The author, the octogenarian reclusive Southern woman who still lives in her Alabama home town, Monroeville, never published another novel.

To Kill a Mockingbird is set in the mid-1930s, in a fictitious small town, Maycomb, Alabama, during the Depression years of "Jim Crow" laws ensuring racial segregation and discrimination against African Americans. Its title relates to the instruction given by attorney Atticus Finch that, while his children can shoot with their air rifles any number of bluejays (this is the gun-toting South), they must never shoot a mockingbird, since they "'don't do one thing but sing their hearts out for us'". The novel relates the legal defence by single-parent Atticus of an innocent black man (the symbolic mockingbird), Tom Robinson, accused of rape by a poor "white trash" girl, Mayella Ewell, whose racist father Bob has abused her. The story is told from the adult perspective of Atticus's tomboy daughter, Scout, who observes the trial with her brother, Jem, and dare-devil friend Dill (modelled on Lee's friend, Truman Capote).

Despite his respected credentials, and a powerful defence case, in this segregated town Atticus has to accept a guilty verdict by the all-white male jury. Before an appeal, Tom tries to escape from jail and is brutally shot dead. Bob Ewell – indirectly accused by Atticus of his daughter's rape – attempts to kill Scout and Jem, but is dramatically prevented by a figure straight out of Southern Gothic fiction, the reclusive Boo Radley.

Like Margaret Mitchell, another unknown writer who published no sequel or successor to her one bestseller, Gone With the Wind (1936), Harper Lee received the Pulitzer Prize. She was grandly fêted and photographed for Life magazine, with Hollywood directors and Gregory Peck, then withdrew from public life and refused interviews. After disappearing from the media radar for over 40 years, she attracted attention as the sidekick to Philip Seymour Hoffman's Truman Capote in the 2005 film, Capote.

Catherine Keener played the long-term friend who helped Capote research and plan his book, In Cold Blood (work he described with sexist dismissivenesss as "secretarial help"). A year later, Sandra Bullock appeared as Harper Lee in another film about Capote, Infamous. That year, 2006, Lee herself granted one surprise interview to the New York Times, speaking only about a writing competition she adjudicates annually at the University of Alabama.

The American South has long been the focus of US and global fears, desires and Gothic fantasies. The site of the nation's worst excesses of slavery, the bloody battlegrounds of the 19th-century Civil War and 20th-century civil-rights brutalities, it has also spawned some of the nation's most brilliant books and films. Blessed with substantial novels and plays that have been adapted into acclaimed films, the South's history and socio-political complexities have been explored and celebrated with popular success. Gone With the Wind, A Streetcar Named Desire, Roots, The Color Purple – and of course To Kill a Mockingbird - have been done proud by directors, actors and Academy Awards.

Harper Lee was well aware of the generic range of Southern literature – the plantation and sentimental novel (Alabama's Augusta Evans Wilson's Beulah and St Elmo), the Gothic (Tennessee Williams's Cat on a Hot Tin Roof) and the sensational (Erskine Caldwell's Tobacco Road) – and she claimed all she wanted to be was "the Jane Austen of South Alabama", focusing on "small-town middle-class southern life". This is ironic or disingenuous, and Mockingbird is no Southern version of Little House on the Prairie. Indeed, the novel defines itself within or against Southern genres, playing with readers' expectations and alluding to the many class, race and gender hypocrisies, inequalities and cruelties of small-town American life.

Although set 30 years earlier than its publication date, the novel was immediately understood as commentary on the series of significant lawsuits about race that culminated in the great civil-rights acts of the 1960s. There are two notorious cases that haunt this work. First is Alabama's Scottsboro case of 1931, in which – following a blatantly unfair trial – eight black teenagers received the death penalty in Alabama for raping two white girls. Second is the shocking murder of the 14-year-old African American Emmett Till, in Mississippi in 1955, for whistling at a white woman – widely regarded as a major spur to the civil-rights movement.

Most important was the groundbreaking 1954 Brown vs Board of Education case. The US Supreme Court over-ruled the "separate but equal" education provision of the previous half-century, and precipitated wider challenges to discrimination – not least the great Montgomery Bus Boycott of 1955-56 in Harper Lee's state, Alabama.

While non-violent direct action undermined the complacency of a racist South, the courtroom became the nation's imaginative debating chamber for issues of racial justice and equality. So, as civil rights activism exploded in the early 1960s, with violent racist battles seen on TV screens, the public developed a huge appetite for courtroom dramas. Both courtroom drama and threatened lynching feature in Mockingbird. Atticus's magisterial final speech to the jury challenges social and racial inequality from the perspective of rational justice and morality.

The book's publication was hailed by The New York Times as a favourable contrast to "morbid, grotesque tales of southern depravity"; in Britain, the Times Literary Supplement agreed that the Finch family were "an oasis of enlightenment in a district rampant with all the old Southern vices".

Yet, as critic Alice Hall Petry wryly observes, critics praising this wholesome family book seemed to overlook its "false accusation of rape, the shooting (seventeen times) of an innocent black man, the acknowledgment of actual incestuous rape, the attempted murder of children, the stabbing to death of the would-be murderer, a man kept prisoner in his own home, and a lynch mob... a morphine addict.. and a boy calling his well-meaning teacher a 'snot-nosed slut'". It is surprising, then, that this hard-hitting novel is usually accorded only a short footnote or brief reference in critical studies of Southern, and indeed American literature. There is only one serious biography, by Charles J Shields, and the first collection of original essays, Hall Petry's On Harper Lee: Essays and Reflections, appeared as late as 2007.

Curiously, this novel and film have attracted far more scholarship by lawyers than literary or film critics, including an entire issue of Alabama Law Review in 1994. Lee herself studied law and the novel has been the focus of many debates about the role of the profession and in particular the nature of the disinterested or engaged lawyer in matters of social and racial importance.

Atticus Finch was hailed as a paragon of virtue, whose cool integrity ensured that the law stood for all that was wisest and best in a divided society. His often-quoted words to Scout are used to exemplify the model legal system: "You never really understand a person... until you climb into his skin and walk around in it." The "law and literature" movement has embraced this novel's example of legal storytelling, offering competing voices and narratives that contribute to a story and judgement. Atticus's behaviour – especially in his summation, when he appeals emotionally to the jury – bridges the professional detachment and empathy gap, now a familiar feature in legal fiction, TV and film, as the human failings - and messy lives and inconsistencies of lawyers - offer a more unstable version of justice.

In recent years this idealisation of Atticus Finch has been challenged. He is accused of having an élitist and paternalistic attitude towards his client and women, while some have asked how this "father-knows-best" could have so casually overlooked the Depression South's appalling record of racism, sexism and class exploitation.

But, to me, re-reading after many years, the myopia of Atticus, his townsfolk and children, all read historically true, and reveal – through their inconsistencies, crass judgements, and unthinking prejudices – the crisis facing the segregated South of the 1930s and the urgent need for a transformation of racial, gender and class roles and expectations in the late 1950s.

Harper Lee observed clearly and wrote prophetically. For all the novel's occasional sentimentality and whimsy, she produced a powerful indictment of American racial history at a crucial moment, one which remains relevant to today's multi-cultural US. This book deserves its long-standing success.

Helen Taylor is professor of English at Exeter University, and author of 'Circling Dixie: contemporary Southern culture through a transatlantic lens'