Iwakuma strained a tendon in the middle finger of his right hand when he caught the finger trying to retrieve a ball from some netting while working out Jan. 20 in Southern California.
The injury did not require surgery, but Iwakuma wore a splint and was not allowed to resume throwing until late March.
Iwakuma is making his return despite only one rehab start (Sunday with Triple-A Tacoma) and "80 percent" command and feel for his pitches, The Seattle Times reported.
The Mariners originally wanted Iwakuma to start Friday night at Houston, the Times reported, but adjusted the plan after Wednesday's game against the New York Yankees was rained out.
Iwakuma finished third in American League Cy Young Award voting last season after posting a 14-6 record and a 2.66 ERA with 185 strikeouts.
The Associated Press contributed to this report.