| Honorific Prefix: | Saint |
| Fiachna | |
| Birth Place: | Desies, Munster |
| Residence: | Lismore, County Waterford, Munster |
| Death Date: | 630 |
| Feast Day: | 29 April |
Saint Fiachna (or Fiachan, Fiachina, Fianchne; died 630) was an early Irish monk who was venerated as a saint. His feast day is 29 April.
The name Fiachna (or Fiachra, Fiacha, Fiachnae, Fiach, Fechín, Feichín) comes from the Old Irish fiach, which means raven. It was given to several legendary and early historical characters. Fiachna is mentioned as a disciple of Mo Chutu of Lismore (Carthagh the younger) in Lismore, County Waterford, in the Life of St. Mochuda of Lismore. Saint Fiachna or Fechno of Agha-luing may be this saint, or may be another whose feast day in 13 March.
The hagiographer Alban Butler wrote,
A passage in the Life of St. Mochuda of Lismore refers to Fiachna: