Chicago announced the trade Monday and will be sending Detroit a player to be named later or cash as part of the trade as well. To open a spot on the 40-man roster, right-hander Dylan Floro was designated for assignment.
Wilson, who turns 30 next month, bolsters a bullpen that has struggled after the All-Star break but had a great weekend in a series win over the Milwaukee Brewers. Wilson will slot in before Cubs closer Wade Davis, as his ability to get out lefties and righties throughout the order was attractive.
"I've seen Wilson pitch in the past, in the American League. Always liked his stuff. How could you not?" manager Joe Maddon told ESPN on Monday. "Alex is a wonderful catcher. He's always been good. He's a very good clutch hitter. Both of them add a lot of veteran presence to our already existing good group.
"When you get another guy like Justin, what it permits you to do is rotate the stock a little bit and not burn anyone out."
Wilson has compiled a 2.68 ERA, 0.94 WHIP and 3.44 strikeout-to-walk ratio (55-16) in 41 appearances for the Tigers this season. He is 13-for-15 in save opportunities after taking over the closer role from struggling Francisco Rodriguez in early May.
The trio of lefties also helps in anticipation of a potential first-round playoff matchup with the Washington Nationals, who feature dangerous lefty hitters Bryce Harper and Daniel Murphy. Wilson has a career .658 OPS versus left-handed hitters and a .606 mark against righties.
The addition of Avila plugs a hole left when the Cubs traded veteran catcher Miguel Montero to the Toronto Blue Jays after he publicly criticized a teammate. Montero was replaced by rookie Victor Caratini, who homered to win the game Sunday, but the team wanted a more veteran presence for the stretch run, hence the addition of Avila.
Avila, the son of Tigers general manager Al Avila, has played all but one of his nine major league seasons in Detroit. He is batting .274 with 11 home runs and 32 RBIs.
During the All-Star break, the Cubs acquired lefty starter Jose Quintana for the top two prospects in their system, and they now have added a lefty reliever and lefty-hitting catcher.