As a concert singer he sang a wide repertoire but drew particular acclaim for his performances in the works of Johann Sebastian Bach and George Frideric Handel.
McCollum made his first concert appearance in New York City as the tenor soloist in a production of Felix Mendelssohn's Elijah at the Church of the Ascension in November 1951 with soprano Beverly Wolff and bass-baritone Paul King.
[2] That same year he made his Carnegie Hall debut singing Prince Vasiliy Ivanovich Shuysky in a concert version of Modest Mussorgsky's Boris Godunov with conductor Dimitri Mitropoulos and the New York Philharmonic.
That same year he made his first appearance with the Boston Symphony Orchestra as the tenor soloist in Hector Berlioz's Roméo et Juliette with soprano Jennie Tourel.
He sang frequently with the Boston Symphony Orchestra under conductor Charles Munch, often at the Tanglewood Music Festival, performing works like the role of the evangelist in Bach's Johannes Passion (1956).
[8] In March 1955 he sang Helenus in a lauded production of Berlioz's Les Troyens with the New England Opera Theater opposite Eunice Alberts as Cassandre, Marriquita Moll as Dido, and Arthur Schoep as Aeneas.
In April of that year he was the tenor soloist in Haydn's The Creation with sopranos Adele Addison and Louise Natale, baritone Mack Harrell, the New York Philharmonic, and conductor Robert Shaw.
[18] Then in December he recorded the role of King Kaspar in Gian Carlo Menotti's Amahl and the Night Visitors in a television production made by the NBC Opera Theatre.