"It was a tough decision to make," the 29-year-old was quoted as saying by ESPNCricinfo.
"I have always loved playing red-ball cricket but I have decided that I would, in future, like to concentrate on white-ball cricket to make sure that I am in a position to give myself the best opportunity to play for the Proteas in the format that I love," he added.
"This is an important decision for me, especially with the World Cup looming next year. I will also be available to play for the Dolphins in all limited-overs competitions and will give it my all to help them win trophies this season."
Miller has represented South Africa in 109 ODIs and 61 T20Is, but hasn't played any Test cricket. In 63 first-class matches, he has scored 3342 runs at an average of 36.32, with six centuries.
"At the age of 29, he still has many years of good cricket left in him in all formats but at the same time, we have to understand that he wants to throw his full weight into helping the Proteas to win the ICC World Cup," Moroe said.
"He has time on his hands to resume his first-class career in due course and I sincerely hope that we have not seen the last of him in red-ball cricket where he has shown his undeniable talents in the past."
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)