Born and raised in the Atlantic coastal community of New Bedford, Massachusetts, he enlisted in the United States Marine Corps in October 1953. While in the Marines, he first became enamored of "imaginative literature" and began to compile A Checklist of the Ballet Scores of Cesare Pugni, eventually published in 1961 as Vol. VIII of Enciclopedia dello Spettacolo. Following his honorable discharge at the rank of sergeant in August 1956, he moved to California, where he enrolled at the University of California, Los Angeles; during this period, he engaged in the concomitant study of classical ballet, working under David Lichine and Tatiana Riaboushinska for a year. In 1958 and 1959, he visited Smith's home in Monterey, California; during these two excursions, Smith introduced him to the oeuvre of George Sterling. After graduating from UCLA in January 1961 with a B.A. in French and the death of Smith in August of that year, Sidney-Freyer commenced work on the poetry that would eventually comprise Songs and Sonnets Atlantean (1971) and The Emperor of Dreams (1976), a bibliography of Smith completed in 1965. From 1965 to 1971, he edited three volumes of Smith's work for Arkham House, a task he would reprise for Pocket Books a decade later.
In 1969, he married Gloria Kathleen Braly, and started giving dramatic readings shortly thereafter at universities and other institutions, almost always incorporating material by Smith and Spenser. His poetry has continued to appear in a variety of weird fiction and speculative poetry-oriented journals.
Sidney-Fryer's verse is marked by a strong imagination, and a Francophilic focus. He is a strong believer in "pure poetry," and practices formalist verse, having developing his own specific poetic form: the Spenserian stanza-sonnet.
He remains a prolific historian of 19th century ballet, and is an expert on the ballet theatre of the romantic era.