The book tells of Sartre's early life, and his growing fame in the period before the 2nd World War. His politics were essentially anti-authority, and so he was wary of becoming too deeply involved in political organisations. During the War Sartre was involved in the resistance, in particular in writing plays with a subtle political message - it seems that it was subtle enough to get past the censors, but unfortunately too subtle for most of the audience as well. In the post-War period Sartre was active in liberation movements, but found it hard to get his work listened to unless it was in support of Stalinism - there were always plenty of people willing to play 'lefter than thou'.
I found this short book very useful, not only in finding out about the life of Sartre, but also in getting a feel for the nature of intellectual life in the 20th century, including movements which came after Sartre, such as postmodernism.