Nelson Smock Riddle Jr., was born in Oradell, NJ on June 21, 1921. He began his education as a musical arranger in his senior year in high school when he started taking lessons with Bill Finegan, arranger for the Glen Miller Orchestra. During that same year he began his first job playing trombone in his classmates orchestra, Charlie Briggs and the Briggadiers Orchestra. After the Briggadiers folded, Nelson moved on to Jerry Wald's Orchestra and then to Charlie Spivak's Orchestra. In 1943, Nelson left Charlie Spivak's group to join the Merchant Marine Corps Band for over a year. After his enlistment ended he joined the Tommy Dorsey Orchestra, but was forced to leave several months later when he was drafted into the army.

During his time in the army Riddle realized that it was more lucrative to arrange music. After his enlistment ended, he moved to New York and started writing arrangements for Les Elgart and Elliot Lawrence. In December of 1946, Riddle received an offer from Bob Crosby to join him in Los Angeles and write arrangements for him. The job didn't materialize, and Riddle was left without a union card and employment. A few months later, arranger Gus Levene referred Riddle to Henry Russell, musical director for the NBC West Coast Orchestra. Russell hired Nelson as a staff arranger for NBC radio, and one of his first assignments was to contribute to The Sealtest Variety Program. Some of the stars he would write for at NBC would be Dean Martin and Bing Crosby.

In August 1951, Riddle's association with Capitol Records began when he started ghostwriting for two top artists at Capitol Records, Nat Cole and Dean Martin. Riddle's big break came when he was asked to serve as an arranger for Frank Sinatra. Sinatra admired Riddle's arrangements so much that he chose him as his primary arranger. He then became known as one of the best arrangers for contemporary singers of the day, backing many vocalists including: Rosemary Clooney, Billy Eckstine, Keely Smith, Ella Fitzgerald, Peggy Lee, and later Linda Ronstadt.

His biggest hit, Lisbon Antigua, went Gold and was one of several recordings he made that would earn him high accolades. Other song honors include a Grammy Award for his Cross Country Suite album; Grammy's for the Linda Ronstadt albums What's New? and Lush Life; and Down Beat Awards for his work on the film Pal Joey. His score for the 1974 film, The Great Gatsby, earned him an Academy Award. Riddle also served as musical director for television shows, including This is Your Music, The Untouchables, Route 66, Newhart, The Smothers Brothers Comedy Hour, and The Julie Andrews Show. He also scored dozens of motion pictures including Ocean's Eleven, Robin and the Seven Hoods, Paint Your Wagon, On a Clear Day You Can See Forever, El Dorado, Lolita, Pal Joey, High Society, Can-Can, Guys and Dolls, and Paint Your Wagon.