Tucker, 44, accepted the job a few weeks ago, but Smart decided to wait to announce the move until after No. 2 Alabama played No. 1 Clemson on Monday in the College Football Playoff National Championship Presented by AT&T, which the Crimson Tide won 45-40.
Smart, who replaces Mark Richt as coach of his alma mater, worked one season with Tucker on Alabama's staff in 2015. After spending the past 10 seasons on Nick Saban's staff, Smart coordinated the Crimson Tide's defense for the final time Monday.
Tucker replaces former Georgia defensive coordinator Jeremy Pruitt, who left to replace Smart at Alabama. Tucker is credited with helping turn around Alabama's secondary after the Tide lost three safeties before this season. Going into Monday's game, Alabama ranked No. 4 in FBS in pass-efficiency defense (99.47 rating) and No. 18 in pass defense (186 yards per game).
Tucker has a wealth of coaching experience in both the NFL and college football. He was the Chicago Bears' defensive coordinator in 2013-14 and worked in the same capacity with the Jacksonville Jaguars from 2009 to 2012. His best NFL work came during the 2011 season, when the Jaguars ranked sixth in the NFL in total defense, with 313 yards allowed per game. Tucker was also Jacksonville's interim head coach for the final five games of 2011.
Tucker, who started his coaching career as a graduate assistant on Saban's staff at Michigan State in 1997, also coached at Miami (Ohio), LSU Tigers and Ohio State. A native of Cleveland, Ohio, Tucker played defensive back at Wisconsin from 1991 to '95.