- Once worked as a dishwasher, photographer and nightclub doorman.
- Breakthrough role was Jordan Catalano on the acclaimed but short-lived ABC drama My So-Called Life.
- Learned Russian for his role as Vitaly Orlov in 2005 crime drama Lord of War.
- Gained more than 60 pounds for his role as Mark David Chapman, who murdered John Lennon in 1980, in the biopic Chapter 27 (2007).
- Is the lead singer and guitarist for platinum-selling rock band 30 Seconds to Mars, in which his brother Shannon plays drums.
- Is a strict vegetarian.
- 2014, Independent Spirit Awards — Best Supporting Male: Winner
- 2014, Critics' Choice Movie Awards — Best Supporting Actor: Winner
- 2012, Toronto International Film Festival — People's Choice Award--Documentary: Winner
- 2013, Screen Actors Guild Awards — Outstanding Performance by a Male Actor in a Supporting Role: Winner
- 2013, Screen Actors Guild Awards — Outstanding Performance by a Cast in a Motion Picture: Nominee
- 2013, Oscar — Best Performance by an Actor in a Supporting Role: Winner
- 2014, Golden Globe — Best Performance by an Actor in a Supporting Role in a Motion Picture: Winner
- Cameron Diaz — Ex-fiancée
- Constance Leto — Mother
- Shannon Leto — Brother
- Attended University of the Arts, Philadelphia, Pennsylvania, United States; attended School of Visual Arts, New York, New York, United States
Season 1, Episode 512
- Birth Place: Bossier City, Louisiana, United States
- Birthday: December 26, 1971, Capricorn
- Profession: Actor, Singer