Flacco (21-of-36, 240 passing yards, no interceptions) hooked up with Anquan Boldin for scoring strikes of 3 and 11 yards in the fourth quarter as the Ravens reeled off the game's final 21 points and avenged a loss to the Patriots in last season's conference championship game.
They now advance to Super Bowl XLVII, where they will meet NFC champions San Francisco, who bested Atlanta earlier Sunday.
Ray Rice carried the ball 19 times for 48 yards with a score and Dennis Pitta had a TD grab among his five catches for 55 yards as the Ravens gained the second Super Bowl appearance in franchise history and first since 2000.
Torrey Smith corralled four passes for 69 yards in the victory.
Tom Brady completed 29-of-54 pass attempts for 320 yards with a touchdown, but was picked off twice for the Patriots, who committed three turnovers overall.
Wes Welker caught eight passes for 117 yards with a TD for New England.