He became principal violist in 1939, which position he held until he retired from the Chicago Symphony Orchestra in 1986.
Besides playing the viola, he was a conductor with the Oak Park-River Forest, Wheaton, and Gary symphonies, as well as the Gold Coast Chamber Orchestra.
In 1963, he resigned as conductor of the Oak Park-River Forest orchestra, because Carol Anderson, a talented black female violinist whom Preves had recruited for the symphony, was pressured to resign because of her race.
The president of the orchestra quickly apologized, and urged Preves to continue to conduct the group.
Ernest Bloch dedicated his Meditation and Processional to Milton Preves.