The six-foot, 208-pound Medlock, a native of Fremont, Calif., spent the 2011 season with Hamilton before signing with the NFL's Carolina Panthers on March 6, 2012. Last year, Medlock attended the Oakland Raiders' training camp.
In 2011, Medlock hit 49-of-55 field goal attempts, a club-record 89.1 per cent success ratio. He also averaged 41.6 yards per punt and was named Hamilton's top special-teams player.
"Justin is a big addition to our football team," Ticats head coach and GM Kent Austin said in a statement. "He's a proven player who is familiar with our organization and has performed at a very high level."
Medlock also has previous CFL experience with the Edmonton Eskimos and Toronto Argonauts. He also spent time with the Washington Redskins, Detroit Lions, St. Louis Rams and Kansas City Chiefs, who selected Medlock in the fifth round, No. 160 overall, in the 2007 NFL draft out of UCLA.
Medlock has hit on 96-of-111 field-goal tries (86.5 per cent) over his CFL career.
"I'm excited to return to the Tiger-Cats and the CFL," Medlock said. "Winning is a huge priority for me, and I feel this team is in position for long-term success.
"I'm looking forward to contributing in a big way in 2014 and beyond."
Lauther hit on 6-of-10 field goals last season, his first in the CFL, and also averaged 59.8 yards per kickoff.