Anew, Ernst Reuter was elected Lord Mayor of all Berlin. Due to the political and administrative division of the city, his office duties were limited to the three western sectors. Although the SPD in the next elections for the House of Representatives on December 3, 1950, lost around 20 per cent of the votes, Ernst Reuter remained in office. A run-off between Reuter and Walther Schreiber, member of the Christian Democratic Party, concluded in a stalemate. Schreiber stepped down in favor of Reuter who then became "Governing Mayor" and in this function led the coalition of the Social Democratic, the Christian Democratic, and the Free Democratic Party.
In all the years as a Lord Mayor and Governing Mayor of Berlin, Ernst Reuter strived relentlessly to foster the status of West-Berlin from an "island" to a "bulwark of freedom". Due to allied concerns, Berlin could not be integrated as the twelfth federal state into the ambit of the constitution; Reuter's effort, however, contributed greatly to West-Berlins closer connection to the Federal Republic of Germany. A supporter of the "magnet theory", he advocated a political and economic strengthening of the city and the West-linkage of the Federal Republic. At the same time he was concerned about the situation of the people on the eastern side of the Iron Curtain.
Ernst Reuter travelled abroad numerous times, making him - aside from Chancellor Konrad Adenauer (CDU) - the most known and most popular politician of the young Federal Republic in the early 1950s. In his memories, Willy Brandt spoke of a "cast of fortune" that Ernst Reuter steered Berlin through the post-war years: "Experience and character had him make of this task - at once difficult and good - the most that could be made of it."
Ernst Reuter died on September 29, 1953, at the age of 64, his death prompting earnest distress and grief. In the following days hundreds of thousands bid farewell to their mayor. On October 3, 1953, Ernst Reuter was layed to rest at the Waldfriedhof in Berlin-Zehlendorf.