Riaz will be available for the county’s first 10 matches, starting against Lancashire Lightning on July 6.
Riaz said: “I’m really excited to be joining Derbyshire for the Vitality Blast.
“They had a terrific 2017 campaign and from what I’ve heard they want to progress further this year.
“I hope I can play my part in a successful side and use my experience to help the squad in any way I can.”