1895 - Friesenheimer Insel becomes part of Mannheim.
1896 - Population: 94,160.(de)
1897 - Käfertal becomes part of Mannheim.
1899 - Neckarau becomes part of Mannheim.
1900 - Population: 141,131.
20th century
1900s-1940s
1905 - Population: 162,607.
1907
Industriehafen Mannheim (harbour) opens on the Neckar river.
Stadtarchiv Mannheim (city archives) established.
Kunsthalle Mannheim (exhibit hall) built.
SV Waldhof Mannheim (sport club) formed.
Population: 173,424.(de)
1910 - Feudenheim becomes part of Mannheim.
1911
Christuskirche (Mannheim) (church) built.
Population: 200,285.(de)
1912 - Mannheim Firehouse built.
1913 - Rheinau and Sandhofen become part of Mannheim.
1914 - Bachchor Mannheim (choir) formed.
1919 - Population: 229,576.
1924 - Mannheim Hospital (now University Hospital Mannheim) opened on the banks of the river Neckar
1925 - "Neue Sachlichkeit" art exhibition held.
1926 - Airfield established at Neuostheim.
1929 - Wallstadt becomes part of Mannheim.
1930
Friedrichsfeld, Kirschgartshausen, Sandtorf, Seckenheim, Straßenheim become part of Mannheim.
Population: 271,833.(de)
1938
November: Kristallnacht pogrom against Jews.
Landkreis Mannheim (district) formed.
Eisstadion am Friedrichspark (ice rink) built.
1940 - Bombing of Mannheim in World War II begins.
1944
September: Mannheim-Sandhofen subcamp of the Natzweiler-Struthof concentration camp established for Poles deported from Warsaw during the Warsaw Uprising.
2 October: First attempt to escape from the Mannheim-Sandhofen subcamp.
15 December: Three Polish prisoners of the Mannheim-Sandhofen subcamp killed in an Allied bombing.
1945
4 January: Public execution of a Polish prisoner of the Mannheim-Sandhofen subcamp.
February: Some prisoners deported from the Mannheim-Sandhofen subcamp to forced labour in Kochendorf.
March: Remaining prisoners deported to Vaihingen an der Enz and Kochendorf; Mannheim-Sandhofen subcamp dissolved.
29 March: Americans capture the city.
6 April: Prisoner of War Executive (PWX) Camp No. 1 for liberated Allied POWs established.
June: The PWX Camp No. 1 converted into the Polish PWX Camp No. 1.
July: United States Coleman Army Airfield begins operating.
1946
Mannheimer Morgen newspaper begins publication.
Polish PWX Camp No. 1 converted into the Tadeusz Kościuszko Civilian Guard Training Center, and later renamed to Tadeusz Kościuszko Theater Civilian Guard Training and Replacement Center for former Polish POWs.
1947
United States military Benjamin Franklin Village established.
8 November: Polish Tadeusz Kościuszko Theater Civilian Guard Training and Replacement Center dissolved.
1949 - Mannheim Waterways and Shipping office established.