Trotter was tracked down in New York and offered the job as Crosby's orchestra leader. Trotter accepted, and took over for Dorsey on the 8 July 1937 broadcast. Soon he was arranging and conducting for Crosby's Decca recordings as well. Their first Decca session was the up-tempo "It's the Natural Thing to Do," recorded July 12, 1937.

Trotter arranged and conducted for Crosby for 17 years. During that time several members of his orchestra went on to greater fame. Jerry Colonna (1905-86) was Trotter's trombonist when his comedic skills were discovered. While playfully singing "On the Road to Mandalay" with Trotter at the organ, Colonna began on a high note reminiscent of an air raid siren and went up from there. The next week he was featured as the guest "concert star" on the Kraft show. Soon Colonna joined Bob Hope's radio show as his comedy side-kick.

Trotter hired Spike Jones (1911-65) in 1937 to beat the drums in his orchestra. Jones became a celebrity during World War II when he moonlighted on a novelty song called "Der Fuhrer's Face." The song became such a hit that Jones left the Trotter orchestra late in 1942 to make a career for himself as conductor of a not-so-serious band, the City Slickers. Jones' raucous sound was invented by Trotter's orchestra to accompany (and cover) the dischordant notes of comedian Bob Burns on the bazooka. Later Jones and his City Slickers returned as guests on the Crosby show. After the City Slickers accompanied Bing on a song, Crosby was heard to say, "John Scott, don't ever leave me!"

Trotter remained as Crosby's musical director until 1954. Their last recording together was "In the Good Old Summertime" in May. That summer Bing decided to end his big-budget radio variety show and with it went his need for a full-time musical director. Bing wrote Trotter on Sept. 9: "I certainly hate to see the wonderful organization we have break up, and it gives me a wrench to be an instrument in its dissolution. I shall never forget all the good years you and I had together, and all the wonderful unselfish things you did for me and my interests. You had a great deal to put up with at times, and your patience and forbearance was always incredible. You must know how grateful I am to you for everything that you have done."

Trotter moved on to television, becoming musical director for the George Gobel show from 1954-60. He remained friends with Bing and was a frequent visitor to Bing's home, even helping redecorate Bing's San Francisco mansion. Trotter worked again as musical director for Bing on his 1964-65 ABC sitcom, "The Bing Crosby Show." Later he directed the music for the Charlie Brown cartoon specials. In 1970 Trotter was nominated for an Oscar and a Grammy for his musical score for the movie A BOY NAMED CHARLIE BROWN.

Bing once said of Trotter, "I'm not musically educated enough to really describe what he was in music terms. I just knew he was very good and he had marvellous taste."

Trotter died of cancer October 30, 1975, a month after arranging a Boston Pops special for PBS