Yes, he did. But it's my understanding that when Rudolf Hess joined the Nazi Party, he brought the idea of Lebensraum with him. Hess was a Nazi Party member before Mein Kampf was written.
Couldn't he just as easily have gotten the idea from Rosenberg and others? True, "The final elaboration of Hitler's programme for acquiring
Lebensraum occurred while he wrote
Mein Kampf during 1924-1925. Essentially, this involved his study of 'geopolitics', that is, the impact of the environment on politics, which provided him with a quasi-scientific justification for the plans he had already worked out. During his period in Landsberg prison (where he had been incarcerated following the failure of his notorious Munich beer hall coup in November 1923), he read and discussed Ratzel's work and other geopolitical literature provided by a Munich Professor of Geography, Karl Haushofer, and fellow-prisoner Rudolf Hess."
http://www.bbc.co.uk/history/worldwars/wwtwo/hitler_lebensraum_01.shtml But this was only an elaboration of a concept that Hitler already had:
"To begin with he was not hostile towards Russia, and saw Britain and France as Germany's main enemies. Indeed, during 1919, he blamed Germany's pre-war politicians for supporting Austria-Hungary against Russia.
"But by 1920 he was arguing that 'an alliance between Russia and Germany can come about only when Jewry is removed', and, by 1924, when he came to write
Mein Kampf, he had concluded that Russia would be the target for Germany's drive to acquire
Lebensraum. So how did this change of approach come about?
"Hitler's views on Russia during these early years were strongly influenced by Alfred Rosenberg, who had joined the Nazi party in 1920 and became the editor of its newspaper, the
Völkischer Beobachter. Rosenberg was a Baltic German who was studying in Moscow when the Russian Revolution broke out in 1917, and left Russia for Germany in November 1918.
"Thus he had experienced the Bolshevik revolution at first hand and became convinced that it was the work of the Jews. Hitler considered Rosenberg an expert on Russia and became equally persuaded of the link between Bolshevism and the Jews.
"By 1922, it was becoming apparent that the Bolshevik regime in Russia was there to stay. Indeed, it is clear from an interview Hitler gave in December 1922 that by then he had decided that an alliance with a Bolshevik Russia was out of the question. Germany would be better off working with Britain and Italy, which appeared to be resisting French hegemony in Europe, against Russia, which could in turn provide Germany's necessary
Lebensraum. Hitler's views on Russia had been further hardened by his contacts with Baltic German exiles in Munich. Notable among these was Max-Erwin von Scheubner-Richter, a contact of August Winnig, the German Commissioner in the Baltic provinces responsible for organising the Free Corps, and General Ludendorff, the former leader of
Oberost.." Ibid.
Now maybe Hess had already introduced the concept to Hitler by 1922, before their stay in prison. But it still seems to me at least as likely that Hitler got it from Rosenberg or other Baltic German exiles from Russia.