| Election Name: | 2009 Dublin South by-election |
| Country: | Ireland |
| Type: | presidential |
| Ongoing: | no |
| Previous Year: | 2007 general election |
| Election Date: | 5 June 2009 |
| Next Year: | 2011 general election |
| Turnout: | 52,479 (57.8%) |
| 2Blank: | Percentage |
| Nominee1: | George Lee |
| Party1: | Fine Gael |
| 1Data1: | 27,768 |
| 2Data1: | 53.4 |
| Nominee2: | Alex White |
| Party2: | Labour Party (Ireland) |
| 1Data2: | 10,294 |
| 2Data2: | 19.8 |
| Party3: | Fianna Fáil |
| 1Data3: | 9,250 |
| 2Data3: | 17.8 |
| Party4: | Green Party (Ireland) |
| 1Data4: | 1,846 |
| 2Data4: | 3.5 |
| Party5: | Sinn Féin |
| 1Data5: | 1,705 |
| 2Data5: | 3.3 |
| Party6: | Independent politician |
| 1Data6: | 650 |
| 2Data6: | 1.2 |
| Nominee7: | Frank O'Gorman |
| Party7: | Independent politician |
| 1Data7: | 351 |
| 2Data7: | 0.7 |
| Nominee8: | Noel O'Gara |
| Party8: | Independent politician |
| 1Data8: | 172 |
| 2Data8: | 0.3 |
| Map Size: | 150px |
| TD | |
| Before Election: | Séamus Brennan |
| Before Party: | Fianna Fáil |
| After Election: | George Lee |
| After Party: | Fine Gael |
A by-election was held in the Dáil Éireann Dublin South constituency in Ireland on Friday, 5 June 2009,[1] following the death of the Fianna Fáil Teachta Dála (TD) Séamus Brennan on 9 July 2008. As Brennan was a Fianna Fáil TD, that party had the responsibility of deciding when the by-election should take place. It was held on the same day as the 2009 European and local elections.[2] There was no legal requirement on when to hold a by-election in Ireland in 2009 but it was generally held within six months.[3] A by-election in the Dublin Central constituency was held on the same date.
Eight candidates contested the vacant seat, with victory going to the Fine Gael candidate, George Lee who was elected on the first count.[4]
George Lee resigned from Dáil Éireann on 8 February 2010 after serving 8 months as a TD.[5]