He played in many international tournaments. In 1904 he tied for 12-13th in Coburg (DSB Congress, Hauptturnier A). In 1905/06 he took 2nd in New York. In 1907 he took 21st in Carlsbad (Akiba Rubinstein won). In 1908 he took 14th in Vienna (Oldřich Duras, Géza Maróczy and Carl Schlechter won), and took 8th in Düsseldorf (Frank Marshall won). In 1909 he took 4th in Berlin. In 1911 he tied for 19th-21st in Carlsbad (Richard Teichmann won).
He was individual best alongside with Rudolf Spielmann at the strong Scheveningen tournament 1923, organised to celebrate 50th anniversary of The Royal Chess Federation, above players like Richard Réti, Géza Maróczy, Jacques Mieses, Edgar Colle, Frederick Yates, or young Max Euwe (20 players). A brand new system was introduced in this event, which since then is known as the 'Scheveningen system' after the suburbs of Hague where the tournament took place. Every player from the first team played against every player of the second team (i.e. Foreigners versus The Netherlands). Paul Johner remained the only unbeaten player, scoring 8.5/10.
He triumphed at the Trieste International Festival 1923 (organized as a singular invitation tournament), finishing clear first in the top group ahead of 2. Esteban Canal, 3. Frederick Yates, 4. Siegbert Tarrasch, 5. Stefano Rosselli, 6.= Lajos Asztalos, etc. (12 players).
His maybe most notable victory came at Berlin 1924 (Quadrangular), when he won ahead of Akiba Rubinstein, Richard Teichmann, and Jacques Mieses.
Subsequently, in January 1925, Paul Johner was ranked as no. 10 of the world according to the retrospective (historical) chessmetrics ratings.