Adolf Hitler's "final solution of the Jewish question" was implemented by Heinrich Himmler in 1942, well after about a million Jews had already been killed at the hands of the Nazis. According to sources, the date can be pinpointed to on or about the time of the Wannsee Villa conference, held in Berlin on January 20, 1942. Marshall Goring had already given written permission concerning "the solution of the Jewish problem" about six months earlier, and the Wannsee conference finalized the decision to utilize extermination camps for the surviving Jews. Minutes to the conference were discovered by the Allies in 1947. Known as "Operation Reinhard" (named after conference chairman Reinhard Heydrich), it dictated that
... the practical execution of the final solution of the Jewish question has fortunately been established by now, and since there is a full agreement on the part of all agencies involved. I would like to ask you at the request of the Reich Marshal to make one of your specialist officials available for the necessary discussion of details in connection with the completion of the draft that shows the organizational, technical and material prerequisites bearing on the actual starting point of the projected solutions.
By summer 1942, the plans were in full force. Administrated by Adolf Eichmann, the first camps with gas chambers at
... Treblinka, Bełżec, and Sobibór, were constructed during Operation Reinhard (October 1941–November 1943), for the extermination of Poland’s Jews.
There is no answer to this that is accepted by all scholars. The most usual answer would be that the Final Solution was authorized at the Wannsee Conference of January 1942. However, there are serious issues with this answer.
The Wannsee Conference seems to have been of some major importance in the planning of the Holocaust. There were important leaders present and the notes taken of the meeting suggest that fundamental questions were discussed about what would be done with the Jews.
However, there are clear issues with saying that the Final Solution was first authorized at this conference. For example, there was at least one death camp already operating and another under construction when this conference occurred. There had also been mass shootings of Jews in Russia.
Overall, then, we cannot be sure when the Final Solution was formally authorized. The usual answer is that this happened at the Wannsee Conference, but there are clear problems with that answer.
Heydrich Himmler was given full authority to pull all possible resources together from different agencies to carry out the Final Solution. It was singled out as the top national priority and the man authorized to conduct it was given full executive power to do so. He directed the leaders of the major departments or agencies of the German state to submit their plans for the elimination of the Jews to him, and in response, presented his own solution to the issue during the Wansee Conference. It was during the conference itself that the establishment of death camps under the explicit aim of fulfilling the goals of the Final Solution was authorised.