In a runoff election, Geisel defeated the previous Christian Democratic mayor Dirk Elbers by gaining 59.2% of the votes.

[3] For the local elections on September 13, 2020, Geisel was again chosen by the SPD as the top candidate for the Düsseldrorf City Council and as a candidate for the office of mayor with 95.5% To warn young people to comply with the regulations of the Corona Protection Ordinance Geisel produced a video with rapper Farid Bang and gained nationwide attention.

Thomas Geisel lost the office as mayor in the second round of the Düsseldorf communal election on September 27, 2020, He got 44,0 % of the votes, his opponent Stephan Keller reached 56,0%.

Geisel appeared at the newly formed party's press conference on January 8, 2024 and indicated that he was seeking political office with the BSW at 2024 European Parliament election.

[7] In late 2017, Geisel came under intense international criticism for canceling an exhibition about the Jewish art dealer Max Stern, who was forced to liquidate his gallery in Düsseldorf after the Nazis took power before World War II.