In the Legends continuity, we first see a "Forcesaber" in the *[Star Wars: Dawn of the Jedi][1]* series, which takes place about 26,000 years before the Battle of Yavin. 

[![Dawn of the Jedi: Force Storm][2]][2]

We see our first true lightsaber in *Star Wars: The Old Republic*, appropriately titled the "[First Blade][3]." It was much older than the Republic (founded approximately 25,000 BBY), but its exact age is unknown.

[![First Blade][4]][4]

In regular canon, the first lightsaber we see is Qui-Gon Jin's (by a spit-second) in *The Phantom Menace.*

[![*Phantom Menace* lightsaber][5]][5]


  [1]: http://starwars.wikia.com/wiki/Star_Wars:_Dawn_of_the_Jedi
  [2]: https://i.sstatic.net/DSSki.jpg
  [3]: http://starwars.wikia.com/wiki/First_Blade
  [4]: https://i.sstatic.net/lZWmb.png
  [5]: https://i.sstatic.net/BZB0z.jpg