His parents were Richard J.and and Emma Ennis of Brooklyn. Three of his grandparents were Irish immigrants. Bert had two brothers, neither of whom, like Bert, used the original forms of their names: Frank Leslie, known as Leslie or F. Leslie, a banker, and Richard, known as Harry, whom Bert reported to have been a song-writer and who died at an early age. The family were Roman Catholic, to which religion Bert faithfully adhered.
Bert Ennis was involved with the development of musical accompaniment to silent films.
In his World War II Draft Registration form, Bert described himself as "self-employed" by Bert Ennis Productions c/o Advance Pictures, 630 Ninth Avenue, NY, NY.
Bert spent the latter decades of his life in Roosevelt, Nassau County, NY. He often said that he was writing a history of silent films, but no trace of this work was found after his death. He is buried in Holy Cross Cemetery in Brooklyn.