Rudolf Lehmann began his career as a prosecutor and jurist in Germany in 1921 and, during World War II, rose to Director and Chief of Legal Department (Wehrmachtrechtswesen) (WR) in the High Command of the Armed Forces, with staff general officer rank.  He received a doctorate in law in 1920 at Marburg. His practice, however, was interrupted by the First World War in which he participated as an officer in the reserve. Lehmann was never a member of the Nazi Party.
He entered government service as an Assistant Public Prosecutor in Essen (1921), then was an Assistant in the Reich Post Ministry (January 1922 to February 1925), Judge of Circuit Court (Landgericht) II Berlin; (March 1925 to September 1937) and then Civil Service Employee in the Reich Ministry for Justice; (October 1937 to July 1938).
With the increased military activity, he became President of a Department in the Reich Military Court (July 1938 to September 1944}, including sitting on the tribunal, appointed by Hitler to investigate the charges against General Wernher von Fritsch. Later, he became Ministerial Director and Chief of Legal Department (Wehrmachtrechtswesen) (WR) in OKW (May 1944 to May 1945). His military rank was Generaloberstabsrichter, the equivalent of a Generaloberst (Allied lieutenant general) outside the line of command.
The Nuremberg Military Tribunals' High Command Case dismissed most charges against him, but focused on his participation in preparing the Barbarossa Jurisdiction Order. Based on his own statements, the Tribunal held he had hardened the language over that which was originally proposed by the Army High Command (OKH) drafter. They also examined his role in the Commissar Order, Night and Fog Decree and the Terror and Sabotage Decrees. He had written, concerning the Barbarossa Jurisdiction Order,
The draft of the army comes very near to our own proposals. The only sentence missing is the provision that the courts of the armed forces have no jurisdiction at all over the indigenous inhabitants. General Halder wished to have this jurisdiction maintained for those cases in which the troops have no time for investigations and for the large number of offenses of minor kinds in which execution by shooting is now justified. I have objections to this, shared by General Jeschonnek.
Once we take this step, we must take it fully. Otherwise it is to be feared that the troops will get rid just of those cases which they consider awkward, namely, the doubtful cases by handing them over to the courts. Thus, the outcome will be contrary to the result we aim at.
The Tribunal concluded that Walter Warlimont had endorsed this additional language, but it had not come from Adolf Hitler, Wilhelm Keitel, Alfred Jodl, or the original drafter, Eugen Mueller of OKH, although Keitel signed the final version. Warlimont wrote, however, that he had telephoned Lehmann about the document, and he responded that Keitel had ordered him not to work on it. 
In convicting Lehmann of atrocities against civilians on this count, they observed, it was one of the "most vicious parts of the order. The defendant’s reasons for this provision appear from the documents and his own testimony to have been that in the event such cases were handed over to the courts, the courts would acquit the defendants for lack of evidence; that those acquittals would bring upon the military courts criticism by Hitler to the effect they were too lenient, as he had done with reference to certain decisions made during the Polish campaign. In other words, it is apparent that, in order to avoid criticism of military courts by the Fuehrer, he was ready to sacrifice the lives of innocent people. " They also found him complicit in the Commissar Order, Night and Fog Decree and the Terror and Sabotage Decrees, and sentenced him to seven years in prison.