Milne has represented New Zealand in 40 One-Day Internationals (ODIs) and 19 T20 Internationals.
He was a part of the Royal Challengers Bangalore earlier. He will wear jersey no. 20 for the Mumbai Indians, it said.
Defending champions Mumbai Indians, who have lost their first three games, will now take on Royal Challengers Bangalore, led by Virat Kohli, on April 17 at the Wankhede Stadium here.
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