In July 1924, Landau took 4th at Antwerp. In May 1926, he tied for 4th-5th at Scarborough. In 1926/27, he took 7th at Hastings (Reserve Tournament). In 1927, he took 2nd, behind Richard Réti, at The Hague. In 1927, Landau lost a match against Réti at Rotterdam (+1 –5 =0). In 1927, he tied for 4 th-6 th at ‘s Hertogenbosch. In July 1927, he tied for 2nd-3rd at London (Reserve). In 1927/28, he took 3rd at Hastings (Reserve). In 1928, he tied for 3rd-4th at Amsterdam. In 1928, he took 2nd, behind Weenink, at Amsterdam (Championship). In December 1928, he took 2nd, behind van den Bosch, at The Hague. In 1928, he tied for 1st with van den Bosch at Zwolle. In 1928/29, he tied for 2 nd-3rd with Pitschak, behind Ludwig Rellstab, at Hastings (Reserve B). In February 1929, he took 3rd at Maastricht. In July 1929, he tied for 2nd-3rd with Weenink, behind Euwe, at Amsterdam (8th Dutch championship). In 1929, he tied for 2nd-3rd at The Hague. In 1929/30, he won at Hastings (Reserve B). In February 1930, he tied for 3rd-4th at Amsterdam. In 1930, he took 4th at Antwerp. In August 1930, he took 4th at Rotterdam (Quadrangular).
Landau played and lost some matches: in 1930 against Géza Maróczy (+0 –3 =0) at Amsterdam; in 1930 against Akiba Rubinstein (+0 –3 =2) at Amsterdam; in 1931 against Max Euwe (+1 –3 =2) at Amsterdam; in 1932 against Salo Flohr (+0 –1 =3) at Rotterdam; in 1933 against Rudolf Spielmann (+1 –2 =3) at Rotterdam; in 1934 against Andor Lilienthal (+1 –2 =3) at Amsterdam; in 1934 against Euwe (+1 –4 =1) at Amsterdam. In Autumn 1934, he won (+6 –0 =0), and drew (+4 –4 =2) matches against Johannes van den Bosch.
He represented his adopted country on fourth board at 3rd Chess Olympiad at Hamburg 1930 (+5 –7 =3), and on second board at 7th Chess Olympiad at Stockholm 1937 (+5 –2 =8).
In 1933, he tied for 4th-6th at Scheveningen (Flohr won). In February 1934, he took 2nd, behind Alexander Alekhine, at Rotterdam (Qudragular). In October–December 1935, during the World Championship match between Alekhine and Euwe in the Netherlands, Landau serviced as an official second for Alekhine, like Maroczy for Euwe did. In May 1936, he tied for 3rd-4th at Ostend. In July 1936, he tied for 7th-9th at Zandvoort. In 1936, he lost two matches against Spielmann, at Amsterdam (+0 –4 =4), and at Zantvoort (+1 –3 =3). In 1936, he tied for 4th-6th at Hannover. In October 1936, he tied for 1st with Alekhine at Amsterdam (Quadrangular). In October 1936, he tied for 4th-6th at Amsterdam.
In 1936, he won the 10th Dutch national championship (although the World Champion Euwe did not compete).
In April 1937, he tied for 4th-5th at Ostend. In June–July 1937, he tied for 15th-16th at Kemeri, but won the best game prize. In June 1938, he tied for 5th-6th at Noordwijk. In 1938, he tied for 5th-6th at Amsterdam (11th Dutch ch.). In November 1938, he was the referee in famous AVRO Tournament. In 1938/39, he tied for 3 rd-4th with Vasja Pirc, behind Szabo and Euwe, at Hastings. In 1939, he tied for 4 th-6th at Amsterdam (KNSB). In 1939, he tied for 1st with Euwe at Amsterdam (VARA). In 1939, he took 3rd at Baarn II. In 1939, he tied for 4th-5th at Barnemouth. In 1939, he drew a match against Theo van Scheltinga at Amsterdam (+3 –3 =4). In 1939, he drew a match against László Szabó at Amsterdam (+2 –2 =6). In 1939, he won at Amsterdam (12th sf Dutch ch.). In 1939, he lost the 12th Dutch championship match against former World Champion Euwe (+0 –5 =5).
During World War II, in 1940, he won at Baarn (Quadrangular), took 4th at Delft (Quadrangular), tied for 3rd-4th at Amsterdam (VAS), tied for 4th-7th at Rotterdam (Kamstra Cup), and tied for 1st-3rd with Nicolaas Cortlever and Lodewijk Prins at Leeuwarden. In 1941, he won at Groningen.
Finally, in September 1942, Landau tried to escape the Nazis by fleeing to Switzerland with his family, but they were caught on September 28th in Breda, near the border with Belgium. He was sent to a concentration camp in Gräditz, Silesia, where he died sometime between October 1943 and March 1944, probably 15 November, 1943. His wife and young daughter, whose hiding place was betrayed, were sent to Auschwitz, where they were gassed on October 12, 1944.