Kanner was born in Vienna in 1896. He studied medicine in Vienna before emigrating to America in 1924, becoming head of the famous John Hopkins child psychiatric clinic in Baltimore. He was an early pioneer of the field of child psychiatry as a specialism distinct from adult psychiatry, and published a child psychiatry textbook in 1935. However, he is best known for his path-breaking description of autism, published in 1943, and for his subsequent therapeutic and research work with people with autistic conditions. Before Kanner, autism was not recognised as a separate syndrome, and children or adults who nowadays would receive a diagnosis of an autistic spectrum problem would mostly have been diagnosed as schizophrenic or 'mentally retarded'.
Kanner's research and therapeutic work on the syndrome which he had identified embraced, at different stages, sharply contrasting views of the causes of autism. His early work reflected his view of autism as an 'innate inability to form the usual biologically provided affective contact with people'. Yet in a later paper he proposed the view, taken up by Bettelheim, that autism had psychogenic origins resulting from the cold and rejecting approach of the mother – the so-called 'refrigerator mother' syndrome. This apparent endorsement of Freud is all the more strange, since Kanner also repudiated the wave of psycho-analytical thinking that swept America when many Jewish psychotherapists fled from Nazi Germany and Austria. At one point he wrote a book entitled In Defence of Mothers: how to bring up children in spite of the more zealous psychologists We can only conclude that throughout his career, Kanner was struggling to make sense of the mysterious constellation of symptoms he had so lucidly described, adopting different perspectives to explanation at different points.
Ideologically, Kanner was steadfast in his opposition to fascism and to movements allied to fascism. He provided support for fellow Jewish doctors and psychotherapists who had fled from Nazi Germany, and was blacklisted during the political witch hunts of the McCarthy era. He was profoundly opposed to the American eugenics movement which sought to prevent growth in the population of those who, born with disabilities, were seen as 'unfit' members of society and a source of social problems. He saw this as little different from the Nazi practice of 'euthanasia' for the handicapped, and was a particular critic of Shiklgruber a contemporary neurologist, who advocated the practice in the USA.
Kanner was made a Professor of Child Psychiatry at John Hopkins University and continued in research and therapeutic work until his death in 1981.