The Bucks announced Tuesday they officially signed the veteran and four-time All-Star, who earned second-team All-NBA honors in 2015 and 2016.
Cousins will attempt to boost a Bucks frontcourt that is missing injured center Brook Lopez.
"DeMarcus is incredibly talented, and his size, toughness and experience will help us," Bucks general manager Jon Horst said in a statement. "He will provide added depth to our frontcourt rotation and we look forward to working him into our system."
The Bucks (13-8) have won seven consecutive games but have been dealing with frontcourt issues due to the absence of Lopez, who hasn't played since a season-opening victory over the Brooklyn Nets because of a back injury.
Cousins should help in that regard, even if the 31-year-old forward no longer is in All-Star form.
Cousins holds career averages of 20.4 points, 10.6 rebounds, 3.1 assists, 1.4 steals and 1.2 blocked shots in 606 regular-season games with the Sacramento Kings, New Orleans Pelicans, Golden State Warriors, Rockets and Clippers. He won a gold medal with the 2016 U.S. Olympic team.
The Associated Press contributed to this report.