Mullin, named to the post Thursday, has been a special assistant to General Manager Garry St. Jean since retiring as a player two years ago.
The Warriors had a 35-45 record this season, their best in years.
"I feel this past season I saw major improvement, individually and collectively," said Mullin, who was a five-time all-star. "Some of them started to see that when you well play collectively, your individual performance goes up."
Mullin played in the NBA 16 years, all but three of them for Golden State.