| Election Name: | 2020 Seine-Maritime's 5th constituency by-election |
| Country: | France |
| Type: | presidential |
| Ongoing: | no |
| Previous Election: | Seine-Maritime's 5th constituency#2017 |
| Previous Year: | 2017 |
| Election Date: | 20 September 2020 (first round) |
| Next Election: | 2022 French legislative election |
| Next Year: | 2022 |
| Turnout: | 17.71% (first round) 17.75% (second round) |
| 1Blank: | % |
| 2Blank: | % |
| Nominee1: | Gérard Leseul |
| Running Mate1: | Martine Blondel |
| Party1: | Socialist Party (France) |
| 1Data1: | 6,586 39.94% 1.92% |
| 2Data1: | 11,502 71.61% 2.46 |
| Nominee2: | Jean-Cyril Montier |
| Running Mate2: | Anaïs Thomas |
| Party2: | National Rally (France) |
| 1Data2: | 2970 18.01%0.81% |
| 2Data2: | 4,561 28.39% |
| Nominee3: | Patricia Lhoir |
| Running Mate3: | Paul Bonmartel |
| Party3: | La République En Marche! |
| 1Data3: | 1,767 10.72% |
| Deputy | |
| Before Election: | Bastien Coriton |
| Before Party: | PS |
| Posttitle: | Elected deputy |
| After Election: | Gérard Leseul |
| After Party: | PS |
A by-election for Seine-Maritime's 5th constituency was held in September 2020. Politically the seat has remained a solid bastion for the Socialist Party. In 2017 the seat was a rare example of them retaining a seat.
The deputy, Christophe Bouillon was elected mayor of Barentin on 28 May 2020 and resigned from the National Assembly on 18 June because of cumulation of mandates. His substitute, Bastien Coriton, was also elected mayor, in Rives-en-Seine, so resigned from the assembly five days after taking office.[1] A by-election was called for 20 and 27 September 2020.
Gérard Leseul of the socialists was elected in the second round.[2]
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