Deng, 30, held the option for the final season of a two-year deal he signed with the Heat in the aftermath of LeBron James' defection last summer.
Deng shot 35.5 percent from 3-point range and was the Heat's best perimeter defender in 2014-15, but he averaged just 14 points and 5.2 rebounds, which were his lowest numbers since his rookie season.
With Deng's decision, Miami is basically set at small forward. Deng will be the presumed starter, with fellow former Duke star Justise Winslow -- the Heat's first-round pick this year -- and James Ennis backing him up.
ESPN.com's Michael Wallace and The Associated Press contributed to this report.