NFL Network's Albert Breer reports that the deal is worth $48 million, with $21 million guaranteed.
"I'm tremendously happy," Smith said. "I plan on getting rings."
Next season was set to be the final year of Smith's rookie contract. He's now under contract with the Ravens through 2019.
The 26-year-old sustained a season-ending foot injury during Week 8 last season. He had 28 tackles and one interception before the injury.
"I think that his best football is still ahead of him," general manager Ozzie Newsome said. "If he doesn't get hurt in the Cincinnati game last year, I don’t know where he could have ended up at as a player, but he was definitely trending up."
Smith is a former 2011 first-round pick by Baltimore. In 2013, he recorded 58 tackles, two interceptions and three forced fumbles.
- Molly Geary