Beck opposed attempts by Adolf Hitler and the Nazi Party to takeover the army. In 1938, he sent an emissary to London in an attempt to get Neville Chamberlain to promise military action if Germany invaded Czechoslovakia.
When Adolf Hitler discovered that Beck as plotting against the regime and he was removed from office. Replaced by Franz Halder, Beck continued to work closely with other opponents of Hitler including Carl Goerdeler, Wilhelm Canaris, Hans Oster and Ulrich Hassell.
In the early months of 1944 Beck approached Erwin Rommel about joining the July Plot. Rommel refused, criticizing the tactic of assassination claiming that it would turn Adolf Hitler into a martyr. Instead he suggested that he should be arrested and brought to trial.
Suspected in being involved in the July Plot, Beck was arrested by on July 20, 1944. General Erich Fromm took him into custody and demanded that he commit suicide. He succeeded only in severely wounding himself and a sergeant finished the job by shooting him in the back of the neck.
Source: Spartacus Educational