Smith, who has served as the Titans' offensive coordinator over the past two seasons, replaces former Falcons head coach Dan Quinn, who was fired along with general manager Thomas Dimitroff in October after a 0-5 start.
Raheem Morris took over as interim head coach and guided the Falcons to a 4-12 overall record.
Under Smith, the Titans ranked fourth in the NFL in scoring during the regular season, averaging 30.7 points per game. Tennessee also ranked third in the league in total yards per game (396.4), and the team finished behind only the Baltimore Ravens in rushing yards per game (168.1) in 2020.
The Titans had a balanced offensive attack under Smith, with star running back Derrick Henry rushing for 2,027 yards this season. Tennessee receiver A.J. Brown recorded 1,075 receiving yards, and teammate Corey Davis finished only 16 yards shy of the 1,000-yard mark.
Smith joined the Titans in 2011 as a defensive quality control coach. He then moved up to multiple other roles within the organization, including offensive quality control coach, offensive line assistant and tight ends coach.
The Falcons interviewed Kansas City Chiefs offensive coordinator Eric Bieniemy, Tampa Bay Buccaneers defensive coordinator Todd Bowles, San Francisco 49ers defensive coordinator Robert Saleh, Carolina Panthers offensive coordinator Joe Brady and Green Bay Packers offensive coordinator Nathaniel Hackett before choosing Smith.